U.S. patent application number 09/793761 was filed with the patent office on 2001-08-30 for apparatus for and method of printing on three-dimensional object.
This patent application is currently assigned to Minolta, Co., Ltd.. Invention is credited to Koreishi, Jun, Kubo, Naoki, Nakanishi, Hideaki.
Application Number | 20010017085 09/793761 |
Document ID | / |
Family ID | 26586229 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017085 |
Kind Code |
A1 |
Kubo, Naoki ; et
al. |
August 30, 2001 |
Apparatus for and method of printing on three-dimensional
object
Abstract
A three-dimensional object printing apparatus according to the
present invention comprises: a shape recognition section for
obtaining three-dimensional shape data about a surface shape of a
three-dimensional object by measurement or the like; an ejection
section for ejecting ink toward the three-dimensional object; a
scanning section for causing the ejection section to scan relative
to the three-dimensional object; and a control section for
controlling an operation of the ejection section and/or the
scanning section in accordance with information about inclination
of the surface of the three-dimensional object, the information
being indicated in the data obtained by the shape recognition
section. The printing apparatus performs printing in accordance
with the information obtained by measurement on the surface
inclination of the object to achieve a high-quality printing
process. More specifically, a mode of operation is determined for
each of a main scanning direction and a sub-scanning direction in
accordance with an inclination angle of an inclined surface with
respect to each of the main scanning direction and the sub-scanning
direction. The printing operation is performed based on the mode of
operation.
Inventors: |
Kubo, Naoki;
(Nishinomiya-Shi, JP) ; Koreishi, Jun;
(Amagasaki-Shi, JP) ; Nakanishi, Hideaki; (Osaka,
JP) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005
US
|
Assignee: |
Minolta, Co., Ltd.
|
Family ID: |
26586229 |
Appl. No.: |
09/793761 |
Filed: |
February 27, 2001 |
Current U.S.
Class: |
101/35 |
Current CPC
Class: |
B41F 17/00 20130101;
B41J 3/4073 20130101; B41J 25/003 20130101; B41J 3/50 20130101;
B41J 2/01 20130101; B41M 5/0088 20130101 |
Class at
Publication: |
101/35 |
International
Class: |
B41F 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2000 |
JP |
P2000-051447 |
Mar 22, 2000 |
JP |
P2000-080191 |
Claims
We claim:
1. An apparatus for providing ink to a surface of a
three-dimensional object, comprising: a shape recognition section
for obtaining data about a surface shape of a three-dimensional
object; an ejection section for ejecting ink toward said
three-dimensional object; a scanning section for causing said
ejection section to scan relative to said three-dimensional object;
and a control section for controlling an operation of said ejection
section and/or said scanning section in accordance with information
about inclination of the surface of said three-dimensional object,
said information being indicated in said data obtained by said
shape recognition section.
2. The apparatus according to claim 1, wherein said scanning
section performs a plurality of continuous main scanning operations
in a predetermined direction, and repeats a sub-scanning operation
for each of said continuous main scanning operations, and wherein
the operation of said scanning section controlled by said control
section is said sub-scanning operation.
3. The apparatus according to claim 1, wherein said ejection
section comprises a plurality of nozzles for ejecting ink, and
wherein the operation of said ejection section controlled by said
control section includes making a predetermined one of said
plurality of nozzles available or unavailable.
4. The apparatus according to claim 3, wherein said control section
makes said predetermined one of said plurality of nozzles available
or unavailable in accordance with a distance between said
predetermined one of said plurality of nozzles and the surface of
said three-dimensional object.
5. The apparatus according to claim 4, wherein said control section
makes said predetermined one of said plurality of nozzles
unavailable when the distance between said predetermined one of
said plurality of nozzles and the surface of said three-dimensional
object is not less than a predetermined value.
6. The apparatus according to claim 1, further comprising an image
data obtaining section for obtaining image data about an image to
be presented on the surface of said three-dimensional object,
wherein said control section controls said ejection section and
said scanning section so that said image data is presented on the
surface of said three-dimensional object.
7. The apparatus according to claim 1, wherein said shape
recognition section measures the surface shape of said
three-dimensional object to obtain said data about the surface
shape of said three-dimensional object, and wherein said shape
recognition section measures an edge part of said three-dimensional
object more precisely than other parts.
8. The apparatus according to claim 1, wherein said shape
recognition section comprises a sensor for measuring the surface
shape of said three-dimensional object to obtain said data about
the surface shape of said three-dimensional object, and wherein
said sensor is caused to scan the surface of said three-dimensional
object along with said ejection section by said scanning section in
order to determine the height of a predetermined point on the
surface of said three-dimensional object with respect to a
predetermined reference plane.
9. The apparatus according to claim 8, wherein said predetermined
reference plane is perpendicular to a direction in which said
ejection section ejects ink, and wherein said scanning section
causes said sensor to scan in two directions parallel to said
reference plane.
10. The apparatus according to claim 1, wherein said ejection
section performs an operation of ejecting ink toward said
three-dimensional object for each polygon of a polyhedron by which
the surface shape of said three-dimensional object is
approximated.
11. The apparatus according to claim 10, wherein the surface shape
of said three-dimensional object is approximated by said polygons,
based on previously given three-dimensional shape model data.
12. The apparatus according to claim 11, wherein the data
obtainment of said shape recognition section, the ink ejection of
said ejection section and the scanning of said scanning section are
performed for each of said polygons.
13. The apparatus according to claim 1, wherein said shape
recognition section comprises a sensor for measuring the surface
shape of said three-dimensional object to obtain said data about
the surface shape of said three-dimensional object, and wherein
said sensor performs an operation of measuring three-dimensional
shape data about said three-dimensional object for each polygon of
a polyhedron by which the surface shape of said three-dimensional
object is approximated.
14. The apparatus according to claim 13, wherein said surface shape
of said three-dimensional object is approximated by said polygons,
based on previously given three-dimensional shape model data.
15. The apparatus according to claim 8, wherein the ink ejection of
the ejection section and the measurement of said sensor are
performed simultaneously while the scanning section causes said
ejection section and said sensor to scan.
16. The apparatus according to claim 1, wherein said ejection
section comprises at least one nozzle for ejecting ink, and wherein
said control section controls the operations of said ejection
section and said scanning section to thereby control ejection
positions of said ejection section.
17. The apparatus according to claim 16, wherein said scanning
section comprises a main scanning section for moving said ejection
section continuously in a predetermined main scanning direction,
and a sub-scanning section for moving said ejection section
stepwise every predetermined travel pitch in a sub-scanning
direction perpendicular to said main scanning direction.
18. The apparatus according to claim 17, wherein said control
section controls a travel velocity of said main scanning section in
said main scanning direction in accordance with inclination of said
three-dimensional object with respect to said main scanning
direction.
19. The apparatus according to claim 17, wherein said control
section controls ink ejection timing of said ejection section in
accordance with inclination of said three-dimensional object with
respect to said main scanning direction.
20. The apparatus according to claim 17, wherein said control
section controls said travel pitch of said sub-scanning section in
said sub-scanning direction in accordance with inclination of said
three-dimensional object with respect to said sub-scanning
direction.
21. The apparatus according to claim 20, wherein said control
section moves said ejection section stepwise every fine pitch in
said sub-scanning direction, and controls said main scanning
section to effect main scanning at a position at which the amount
of movement of said ejection section in said sub-scanning direction
equals said travel pitch.
22. The apparatus according to claim 21, wherein said travel pitch
is variable.
23. The apparatus according to claim 17, wherein, when said
ejection section ejects ink toward a surface inclined with respect
to a plane parallel to said main scanning direction and said
sub-scanning direction, said control section shortens an interval
between said ejection positions in accordance with the degree of
inclination of said surface.
24. The apparatus according to claim 16, wherein said control
section controls the ejection operation for each polygon of a
polyhedron by which the surface shape of said three-dimensional
object is approximated.
25. The apparatus according to claim 17, wherein said at least one
nozzle includes a plurality of nozzles arranged in an array for
ejecting ink, and wherein said scanning section further comprises a
rotative scanning section for rotating a direction in which said
plurality of nozzles are arranged within a plane parallel to said
main scanning direction and said sub-scanning direction.
26. The apparatus according to claim 24, wherein said ejection
section further comprises a plurality of nozzle array members each
including said array of nozzles, each of said plurality of nozzle
array members being in one piece for each ink type, and wherein
said ejection section further comprises a linkage mechanism for
coupling said plurality of nozzle array members with each other to
prevent a positional relationship of said nozzles between said
nozzle array members from deviating in said sub-scanning direction
because of the rotation of said rotative scanning section.
27. A method of providing ink to a surface of a three-dimensional
object, comprising the steps of: (a) obtaining data about a surface
shape of a three-dimensional object; and (b) causing an ejection
section to eject ink toward said three-dimensional object while
causing said ejection section to scan relative to said
three-dimensional object in accordance with information about
inclination of the surface of said three-dimensional object, said
information being indicated in said data obtained in said step
(a).
28. The method according to claim 27, wherein, in said step (b), a
plurality of continuous main scanning operations are performed in a
predetermined direction, and a sub-scanning operation is repeated
for each of said continuous main scanning operations, said
sub-scanning operation being controlled in accordance with said
information about the inclination of the surface of said
three-dimensional object.
29. The method according to claim 27, wherein said ejection section
comprises a plurality of nozzles for ejecting ink, and wherein said
ejection section is controlled to make a predetermined one of said
plurality of nozzles available or unavailable in said step (b).
30. The method according to claim 27, wherein said data about the
surface shape of said three-dimensional object is obtained in said
step (a) by a sensor for measuring the surface shape of said
three-dimensional object, and wherein said sensor is caused to scan
the surface of said three-dimensional object along with said
ejection section in order to determine the height of a
predetermined point on the surface of said three-dimensional object
with respect to a predetermined reference plane.
31. The method according to claim 27, wherein an operation of
ejecting ink toward said three-dimensional object is performed by
said ejection section for each polygon of a polyhedron by which the
surface shape of said three-dimensional object is approximated.
32. The method according to claim 27, wherein said data about the
surface shape of said three-dimensional object is obtained in said
step (a) by a sensor for measuring the surface shape of said
three-dimensional object, and wherein an operation of measuring
three-dimensional shape data about said three-dimensional object is
performed by said sensor for each polygon of a polyhedron by which
the surface shape of said three-dimensional object is
approximated.
33. The method according to claim 27, wherein said ejection section
comprises at least one nozzle for ejecting ink.
34. The method according to claim 33, wherein, in said step (b),
main scanning for moving said ejection section continuously in a
predetermined main scanning direction, and sub-scanning for moving
said ejection section stepwise every predetermined travel pitch in
a sub-scanning direction perpendicular to said main scanning
direction are performed, and a travel velocity of said main
scanning in said main scanning direction is controlled in
accordance with inclination of said three-dimensional object with
respect to said main scanning direction.
35. The method according to claim 33, wherein, in said step (b),
main scanning for moving said ejection section continuously in a
predetermined main scanning direction, and sub-scanning for moving
said ejection section stepwise every predetermined travel pitch in
a sub-scanning direction perpendicular to said main scanning
direction are performed, and ink ejection timing of said ejection
section is controlled in accordance with inclination of said
three-dimensional object with respect to said main scanning
direction.
36. The method according to claim 33, wherein, in said step (b),
main scanning for moving said ejection section continuously in a
predetermined main scanning direction, and sub-scanning for moving
said ejection section stepwise every predetermined travel pitch in
a sub-scanning direction perpendicular to said main scanning
direction are performed, and said travel pitch of said sub-scanning
in said sub-scanning direction is controlled in accordance with
inclination of said three-dimensional object with respect to said
sub-scanning direction.
37. The method according to claim 36, wherein said ejection section
is moved stepwise every fine pitch in said sub-scanning direction,
and said main scanning is controlled to be effected at a position
at which the amount of movement of said ejection section in said
sub-scanning direction equals said travel pitch.
38. The method according to claim 33, wherein said at least one
nozzle includes a plurality of nozzles arranged in an array for
ejecting ink, and wherein the scanning in said step (b) is
performed by a rotative scanning section for rotating a direction
in which said plurality of nozzles are arranged within a plane
parallel to said main scanning direction and said sub-scanning
direction.
Description
[0001] This application is based on applications Nos. 2000-51447
and 2000-80191 filed in Japan, the contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for and method
of printing on a three-dimensional object.
[0004] 2. Description of the Background Art
[0005] A printing apparatus which ejects ink onto printing paper by
an ink jet technique to print a desired image and the like is
conventionally known. In such a printing apparatus, an ejection
head expels ink while continuously moving in a main scanning
direction. Upon completion of printing of one line in the main
scanning direction, the ejection head is moved a fixed distance in
a sub-scanning direction orthogonal to the main scanning direction,
and starts the next printing operation in the main scanning
direction.
[0006] An attempt has been made to print on a three-dimensional
object by using the technique of ejecting ink such as the ink jet
technique.
[0007] However, printing by ejecting droplets of ink from the
ejection head onto the three-dimensional object has a problem such
that the density of dots changes with the surface shape of the
object. More specifically, printing on a portion of the object
which has a near-horizontal surface, like the printing on a surface
of printing paper and the like, provides a high-density dot
distribution, whereas printing on an inclined surface of the object
results in a dot distribution which is sparse depending on the
angle of inclination of the inclined surface.
[0008] FIGS. 36A and 36B show a conventional printing method for
illustration of the above-mentioned phenomenon. FIG. 36A shows a
dot distribution when printed on a horizontal surface, and FIG. 36B
shows a dot distribution when printed on an inclined surface. For
printing on a three-dimensional object, a conventional printing
apparatus moves the ejection head stepwise every fixed distance in
the sub-scanning direction, independently of whether a
to-be-printed portion of the object has a horizontal surface or an
inclined surface. The fixed distance is set at a distance d which
provides a dense distribution of dots printed on the horizontal
surface, as shown in FIG. 36A. Thus, when the to-be-printed portion
of the object has an inclined surface at an inclination angle
.theta. with respect to the sub-scanning direction, the movement of
the fixed distance d of the ejection head in the sub-scanning
direction as shown in FIG. 36B causes a dot-to-dot spacing on the
inclined surface to equal d/cos .theta., resulting in a sparse dot
distribution.
[0009] This phenomenon also occurs in the main scanning direction
in which the ejection head continuously moves. However, the problem
of the above-mentioned phenomenon in the main scanning direction in
which the ejection head continuously moves is relatively easily
overcome by controlling the timing of ejection of ink from the
ejection head or otherwise.
[0010] On the other hand, since the ejection head is driven
stepwise in the sub-scanning direction after the continuous
printing in the main scanning direction, the problem of the
above-mentioned phenomenon in the sub-scanning direction is not
overcome by merely controlling the timing of ink ejection.
[0011] To solve the above-mentioned problem in the case where the
object is inclined with respect to the sub-scanning direction, it
is contemplated to incline the ejection head in accordance with the
inclined surface so that the ink is always ejected in a direction
normal to the inclined surface to perform sub-scanning through the
fixed distance d along the inclined surface. Such an arrangement,
however, increases the complexity of driving mechanisms and
operational control, and accordingly increases the size of the
apparatus.
[0012] For a printing apparatus for printing on a two-dimensional
object (e.g., printing paper), there has been no need to consider
the surface shape of the object which is constant or flat. However,
for printing on the three-dimensional object, it is necessary to
consider the three-dimensional shape of the object to achieve
proper printing.
[0013] In many of the printing apparatuses for printing on the
two-dimensional object (e.g., printing paper), a slight positional
deviation of the printing paper does not become a problem. However,
for printing on the three-dimensional object, a positional
deviation of the object results in improper printing. For example,
when applying different colors to two adjacent faces bordered by an
edge, there is a problem such that a deviation of the coloring
position is very conspicuous to result in remarkable deterioration
of a print quality.
[0014] Thus, the printing on a three-dimensional object is required
to take the three-dimensional shape of the object into
consideration to provide a high print quality.
SUMMARY OF THE INVENTION
[0015] The present invention is intended for an apparatus for
providing ink to a surface of a three-dimensional object. According
to a first aspect of the present invention, the apparatus
comprises: a shape recognition section for obtaining data about a
surface shape of a three-dimensional object; an ejection section
for ejecting ink toward the three-dimensional object; a scanning
section for causing the ejection section to scan relative to the
three-dimensional object; and a control section for controlling an
operation of the ejection section and/or the scanning section in
accordance with information about inclination of the surface of the
three-dimensional object, the information being indicated in the
data obtained by the shape recognition section.
[0016] Thus, the operation of the ejection section and/or the
scanning section is controlled in accordance with the information
about the surface inclination of the three-dimensional object, the
information being indicated in the data obtained by the shape
recognition section. Therefore, the apparatus can perform a
high-quality printing process.
[0017] According to a second aspect of the present invention, in
the apparatus of the first aspect, the scanning section performs a
plurality of continuous main scanning operations in a predetermined
operations, and repeats a sub-scanning operation for each of the
continuous main scanning direction. The operation of the scanning
section controlled by the control section is the sub-scanning
operation.
[0018] Thus, the operation of the scanning section controlled by
the control section is the sub-scanning operation. Therefore, the
apparatus can provide a uniform distribution of dots of ink in the
sub-scanning direction when printing on the three-dimensional
object.
[0019] According to a third aspect of the present invention, in the
apparatus of the first aspect, the ejection section comprises a
plurality of nozzles for ejecting ink, and the operation of the
ejection section controlled by the control section is to make a
predetermined one of the plurality of nozzles available or
unavailable.
[0020] Thus, the predetermined one of the plurality of nozzles is
made available or unavailable. Therefore, the apparatus can eject
ink within tolerance of a target position on the object.
[0021] According to a fourth aspect of the present invention, in
the apparatus of the first aspect, the shape recognition section
comprises a sensor for measuring the surface shape of the
three-dimensional object to obtain the data about the surface shape
of the three-dimensional object. The sensor is caused to scan the
surface of the three-dimensional object along with the ejection
section by the scanning section in order to determine the height of
a predetermined point on the surface of the three-dimensional
object with respect to a predetermined reference plane.
[0022] Thus, the shape recognition section comprises the sensor for
measuring the surface shape of the three-dimensional object to
obtain the data about the surface shape of the three-dimensional
object. The sensor is caused to scan the surface of the
three-dimensional object along with the ejection section by the
scanning section in order to determine the height of the
predetermined point on the surface of the three-dimensional object
with respect to the predetermined reference plane. Therefore, the
apparatus can efficiently obtain the data about the surface shape
of the three-dimensional object.
[0023] According to a fifth aspect of the present invention, the
control section moves the ejection section stepwise every fine
pitch in the sub-scanning direction, and controls the main scanning
section to effect main scanning at a position at which the amount
of movement of the ejection section in the sub-scanning direction
equals a travel pitch.
[0024] Thus, the control section moves the scanning section
stepwise every fine pitch in the sub-scanning direction, and
controls the main scanning section to effect main scanning at the
position at which the amount of movement of the ejection section in
the sub-scanning direction equals the travel pitch. This achieves
efficient printing.
[0025] It is an object of the present invention to provide an
apparatus for and method of printing which can print on a
three-dimensional object with high quality.
[0026] It is another object of the present invention to provide an
apparatus for and method of printing which can constantly provide a
uniform distribution of dots of ink particularly when printing on a
three-dimensional object.
[0027] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is an external view of a printing apparatus according
to a first preferred embodiment of the present invention;
[0029] FIG. 2 shows a positional relationship between an ejection
head and an object to be printed;
[0030] FIGS. 3A and 3B show the principle of providing a uniform
dot distribution in a sub-scanning direction,
[0031] FIG. 3A illustrating printing on a horizontal surface in the
sub-scanning direction,
[0032] FIG. 3B illustrating printing on an inclined surface at an
inclination angle with respect to the sub-scanning direction;
[0033] FIGS. 4A, 4B, 4C and 4D show a specific driving method for
providing a travel distance in the sub-scanning direction,
[0034] FIG. 4A illustrating printing on a horizontal surface in the
sub-scanning direction,
[0035] FIG. 4B illustrating printing on an inclined surface at an
inclination angle of 30.degree. with respect to the sub-scanning
direction,
[0036] FIG. 4C illustrating printing on an inclined surface at an
inclination angle of 45.degree.,
[0037] FIG. 4D illustrating printing on an inclined surface at an
inclination angle of 60.degree.;
[0038] FIGS. 5A and 5B show a first method for ejection pattern
control in a main scanning direction,
[0039] FIG. 5A illustrating printing on a horizontal surface in the
main scanning direction,
[0040] FIG. 5B illustrating printing on an inclined surface at an
inclination angle with respect to the main scanning direction;
[0041] FIGS. 6A and 6B show a second method for ejection pattern
control in the main scanning direction,
[0042] FIG. 6A illustrating printing on a horizontal surface in the
main scanning direction,
[0043] FIG. 6B shows printing on an inclined surface at an
inclination angle with respect to the main scanning direction;
[0044] FIG. 7 is a block diagram of a control mechanism in the
printing apparatus;
[0045] FIG. 8 is a flowchart showing the overall operation of the
printing apparatus;
[0046] FIGS. 9A and 9B show an example of an approximation of the
shape of the object which is made by polygonal faces,
[0047] FIG. 9A illustrating an example of the object having a
smoothly curved surface,
[0048] FIG. 9B illustrating the shape of FIG. 9A approximated by a
plurality of polygons;
[0049] FIGS. 10A and 10B show another example of the approximation
of the shape of the object which is made by polygonal faces,
[0050] FIG. 10A illustrating an example of the object having a
smoothly curved surface,
[0051] FIG. 10B illustrating the shape of FIG. 10A approximated by
a plurality of polygons;
[0052] FIGS. 11A and 11B show still another example of the
approximation of the shape of the object which is made by polygonal
faces,
[0053] FIG. 11A illustrating an example of the object having a
smoothly curved surface,
[0054] FIG. 11B illustrating the shape of FIG. 11A approximated by
a plurality of polygons;
[0055] FIG. 12 shows the rotational operation of the ejection
head;
[0056] FIGS. 13A, 13B and 13C show an example of a multi-nozzle
arrangement of the ejection head,
[0057] FIG. 13A illustrating a nozzle unit of the ejection head as
viewed from the object,
[0058] FIG. 13B illustrating the nozzle unit rotated in accordance
with the inclination angle,
[0059] FIG. 13C being an enlarged view of a portion A shown in FIG.
13B;
[0060] FIGS. 14A, 14B and 14C show another example of the
multi-nozzle arrangement of the ejection head,
[0061] FIG. 14A illustrating the nozzle unit of the ejection head
as viewed from the object,
[0062] FIG. 14B illustrating the nozzle unit rotated in accordance
with the inclination angle,
[0063] FIG. 14C being an enlarged view of the portion A shown in
FIG. 14B;
[0064] FIGS. 15A, 15B and 15C show still another example of the
multi-nozzle arrangement of the ejection head,
[0065] FIG. 15A illustrating the nozzle unit of the ejection head
as viewed from the object,
[0066] FIG. 15B illustrating nozzle array members of the nozzle
unit rotated in accordance with the inclination angle,
[0067] FIG. 15C being an enlarged view of the portion A shown in
FIG. 15B;
[0068] FIG. 16 is a perspective view of the structure of a
three-dimensional object printing apparatus according to a second
preferred embodiment of the present invention;
[0069] FIG. 17 shows a print head section as viewed obliquely from
below;
[0070] FIG. 18 is a schematic diagram showing the construction of
the printing apparatus of FIG. 16;
[0071] FIG. 19 is a functional block diagram of the printing
apparatus of FIG. 16;
[0072] FIG. 20 is a flowchart showing the operation of the printing
apparatus according to the second preferred embodiment;
[0073] FIG. 21 is a top plan view of an object to be printed as
viewed from the -Z direction;
[0074] FIG. 22 is a side view of the object as viewed from the -Y
direction;
[0075] FIGS. 23A, 23B, 23C and 23D show ink ejection control (in
the sub-scanning direction) with ejection nozzle control,
[0076] FIG. 23A illustrating printing on a horizontal part of the
object,
[0077] FIG. 23B illustrating printing on a steeply inclined surface
of the object,
[0078] FIG. 23C illustrating printing on the top of the object,
[0079] FIG. 23D illustrating printing on a gently inclined surface
of the object;
[0080] FIGS. 24A, 24B, 24C and 24D show ink ejection control (in
the main scanning direction) with ejection nozzle control,
[0081] FIG. 24A illustrating printing on a horizontal part of the
object,
[0082] FIG. 24B illustrating printing on a gently inclined surface
of the object,
[0083] FIG. 24C illustrating printing on the top of the object,
[0084] FIG. 24D illustrating printing on a steeply inclined surface
of the object;
[0085] FIG. 25 is a flowchart showing the operation of the printing
apparatus according to a third preferred embodiment of the present
invention;
[0086] FIG. 26 is a flowchart regarding an operation included in
the flowchart of FIG. 25;
[0087] FIG. 27 is a flowchart showing the operation of the printing
apparatus according to a fourth preferred embodiment of the present
invention;
[0088] FIG. 28 is a flowchart regarding an operation included in
the flowchart of FIG. 27;
[0089] FIG. 29 is a perspective view of an object to be printed
which has a triangular cross-sectional configuration;
[0090] FIGS. 30A, 30B and 30C conceptually show the operation of
the fourth preferred embodiment,
[0091] FIG. 30A illustrating the operation of distance measurement
being made on a first segmented region,
[0092] FIG. 30B illustrating the operation of distance measurement
being made on a second segmented region and the operation of
printing being performed on the first segmented region,
[0093] FIG. 30C illustrating the operation of distance measurement
being made on a third segmented region and the operation of
printing being performed on the second segmented region;
[0094] FIG. 31 conceptually shows the relationship between a
distance measurement position and an ink striking position;
[0095] FIG. 32 conceptually shows the relationship between the
distance measurement position and the ink striking position when a
multi-nozzle arrangement is used;
[0096] FIG. 33 is a flowchart showing the operation of the printing
apparatus according to a modification of the present invention;
[0097] FIG. 34 shows a modification of a displacement sensor
mounting position;
[0098] FIG. 35 shows another modification of the displacement
sensor mounting position; and
[0099] FIGS. 36A and 36B show a conventional method of printing on
a three-dimensional object,
[0100] FIG. 36A illustrating a dot distribution when printed on a
horizontal surface,
[0101] FIG. 36B illustrating a dot distribution when printed on an
inclined surface.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0102] Preferred embodiments according to the present invention
will now be described in detail with reference to the drawings.
[0103] <A. First Preferred Embodiment>
[0104] <A1. Overall Construction of Printing Apparatus>
[0105] FIG. 1 is an external view of a printing apparatus 100A
according to a first preferred embodiment of the present invention.
Three mutually orthogonal axes X, Y and Z are defined as those
depicted in FIG. 1 in this preferred embodiment.
[0106] The printing apparatus 100A comprises a base plate 81, a
stage 82 in a central position on the upper surface of the base
plate 81 for placing thereon an object 9 to be printed, and a pair
of grooves 83 extending along the Y axis in the base plate 81
outside the stage 82. The pair of grooves 83 receive a pair of
stands ST, respectively, which are movable along the grooves 83
(i.e. in the Y direction) by a sub-scanning direction driver 20
(See FIG. 7) provided inside the base plate 81. A rail RL is
mounted between upper parts of the respective stands ST, and is
provided with a head holding mechanism 13. A main scanning
direction driver 10 (See FIG. 7) is provided inside the rail RL.
The head holding mechanism 13 is movable along the rail RL (i.e. in
the X direction) by the main scanning direction driver 10. An
ejection head rotation driver 30 (See FIG. 7) is provided inside
the head holding mechanism 13. The head holding mechanism 13
further includes a driver for vertically moving up and down an
ejection head 50. The ejection head 50 moves downwardly for
printing, and moves upwardly for replacement of the object.
[0107] The ejection head 50 is coupled to a lower part of the head
holding mechanism 13 via a rotary shaft AR rotatable by the
ejection head rotation driver 30. The ejection head 50 has a nozzle
unit 51 for ejecting printing ink toward the object 9 by the ink
jet technique or the like. A surface of the nozzle unit 51 which is
opposed to the object 9 is provided with ejection nozzles for
ejecting the ink. An ejection nozzle driver 60 (See FIG. 7) for
driving the ejection nozzles is provided inside the ejection head
50. The ejection nozzle driver 60 causes the ejection nozzles to
eject the ink toward the object 9. In this preferred embodiment,
the ink is ejected vertically downwardly toward the X-Y plane from
the ejection nozzles.
[0108] FIG. 2 shows a positional relationship between the ejection
head 50 and the object 9. The printing apparatus 100A shown in FIG.
1 performs a printing operation while moving the ejection head 50
relative to the object 9 in the X direction used as a main scanning
direction and in the Y direction used as a sub-scanning direction.
More specifically, printing one line in the main scanning direction
X is done by ejecting ink from the ejection nozzles of the ejection
head 50 while continuously moving the ejection head 50 in the main
scanning direction X. Upon completion of the one-line printing
operation in the main scanning direction X, the ejection head 50 is
moved in the sub-scanning direction Y to the next position and
starts the next printing operation in the main scanning direction
X.
[0109] The printing apparatus 100A is designed to control an ink
ejection pattern during the movement of the ejection nozzles both
in the main scanning direction X and in the sub-scanning direction
Y in accordance with an inclination of the object at a position at
which a droplet of ink ejected from an ejection nozzle of the
ejection head 50 strikes the object (i.e. a position corresponding
to the current position of an ejection nozzle of the ejection head
50). This achieves a uniform dot distribution on the object both in
the main scanning direction X and in the sub-scanning direction
Y.
[0110] <A2. Ejection Pattern Control in Sub-Scanning Direction
Y>
[0111] Ejection pattern control in the sub-scanning direction Y
will be described first.
[0112] FIGS. 3A and 3B show the principle of providing a uniform
dot distribution in the sub-scanning direction Y. FIG. 3A shows
printing on a horizontal surface in the sub-scanning direction Y,
and FIG. 3B shows printing on an inclined surface at an inclination
angle .theta. with respect to the sub-scanning direction Y. The
term "horizontal" used herein means being parallel to the Y axis,
and the term "inclined" used herein means not being parallel to the
Y axis. The inclination angle .theta. is the angle of inclination
of the surface of the object 9 with respect to a reference plane of
measurement (X-Y plane herein).
[0113] To provide a dense dot distribution in the sub-scanning
direction Y when printing on the horizontal surface of the object 9
as shown in FIG. 3A, the travel distance of the ejection head 50 in
the sub-scanning direction Y is set at a distance d as in the
conventional manner. As a result, the spacing between dots of ink
on the horizontal part of the object 9 equals d. This provides a
high-definition printing result.
[0114] On the other hand, to provide a dense dot distribution in
the sub-scanning direction Y when printing on the inclined surface
of the object 9 as shown in FIG. 3B, the travel distance of the
ejection head 50 in the sub-scanning direction Y is set at a
distance d cos .theta. depending on the inclination angle .theta..
Starting the printing operation in the main scanning direction X
provides the dot-to-dot spacing which equals d in the sub-scanning
direction Y on the inclined surface. This dot-to-dot spacing is
equal to the spacing d between the dots printed on the horizontal
surface. As a result, a high-definition printing result is obtained
also on the inclined surface.
[0115] In other words, the printing apparatus 100A features a
variable travel distance of the ejection head 50 in the
sub-scanning direction Y, and changes the travel distance of the
ejection head 50 depending on the inclination with respect to the
sub-scanning direction Y when moving the ejection head 50 stepwise
in the sub-scanning direction Y. More specifically, when the travel
distance in the sub-scanning direction Y is d in the case of
printing on the horizontal surface and the inclination angle is
.theta. with respect to the sub-scanning direction, the travel
distance of the ejection head 50 in the sub-scanning direction Y is
set at d cos .theta.. This provides the dot-to-dot spacing which
equals d in the sub-scanning direction Y independently of the
surface shape of the object 9, thereby achieving a uniform dot
distribution.
[0116] FIGS. 4A, 4B, 4C and 4D show a specific driving method for
providing a travel distance (or travel pitch) L of the ejection
head 50 in the sub-scanning direction Y. FIG. 4A illustrates
printing on a horizontal surface in the sub-scanning direction Y,
FIG. 4B illustrates printing on an inclined surface at an
inclination angle of 30.degree. with respect to the sub-scanning
direction Y, FIG. 4C illustrates printing on an inclined surface at
an inclination angle of 45.degree., and FIG. 4D illustrates
printing on an inclined surface at an inclination angle of
60.degree..
[0117] The printing apparatus 100A is constructed to drive the
ejection head 50 to move a fine pitch p as a unit in the
sub-scanning direction Y. The fine pitch p is a minimum unit of
distance the ejection head 50 is driven to move in the sub-scanning
direction Y in the printing apparatus 100A, and is set at a value
smaller than the travel distance L (=d) used for printing on the
horizontal surface. In this preferred embodiment, the fine pitch p
is set at d/10 as shown in FIGS. 4A to 4D.
[0118] In the printing apparatus 100A, a controller 43 (See FIG. 7)
to be described later determines the travel distance L in
accordance with the inclined surface by calculating the cumulative
value of the fine pitch p so that the spacing between dots of ink
to be formed on the inclined surface is closest to the dot-to-dot
spacing d on the horizontal surface and then by defining the
cumulative value as the travel distance L.
[0119] More specifically, when printing on the horizontal surface
of the object 9 as shown in FIG. 4A, the travel distance L is set
at d since the dot-to-dot spacing on the horizontal surface is
required to equal d.
[0120] Next, when printing on the inclined surface of the object 9
which has the inclination angle of 30.degree. as shown in FIG. 4B,
the travel distance L is determined so that the dot-to-dot spacing
on the inclined surface is closest to d. The dot-to-dot spacing on
the inclined surface is approximately 0.92 d when the ejection head
50 moves the fine pitch p eight times to provide the travel
distance L=8 d/10, and is approximately 1.04 d when the ejection
head 50 moves the fine pitch p nine times to provide the travel
distance L=9 d/10. In this case, the travel distance L is set at 9
d/10 which is closest to the dot-to-dot spacing d on the horizontal
surface.
[0121] Next, when printing on the inclined surface of the object 9
which has the inclination angle of 45.degree. as shown in FIG. 4C,
the travel distance L is set at 7 d/10 so that the dot-to-dot
spacing on the inclined surface is closest to d. In this case, the
dot-to-dot spacing on the inclined surface is approximately 0.99
d.
[0122] Next, when printing on the inclined surface of the object 9
which has the inclination angle of 60.degree. as shown in FIG. 4D,
the travel distance L is set at 5 d/10 so that the dot-to-dot
spacing on the inclined surface is closest to d. In this case, the
dot-to-dot spacing on the inclined surface is equal to the
dot-to-dot spacing d on the horizontal surface.
[0123] Therefore, the printing apparatus 100A establishes the fine
pitch p as the unit of distance the ejection head 50 is driven to
move in the sub-scanning direction Y so that the fine pitch p is
less than the dot-to-dot spacing on the surface of the object 9,
thereby to maintain the spacing in the sub-scanning direction Y
between the dots of ink even on the inclined surfaces at an
approximately fixed value. This accomplishes fine-definition
printing also in the sub-scanning direction.
[0124] Two modes of operation are contemplated when actually moving
the ejection head 50 relative to the object 9 to perform
printing.
[0125] A first mode of operation is such that the ejection head 50
is driven in the main scanning direction X each time the ejection
head 50 is moved stepwise the fine pitch p in the sub-scanning
direction Y. In this mode, when moving the ejection head 50
relative to the object 9, the main scanning direction driver 10 and
the sub-scanning direction driver 20 may be adapted to repeatedly
drive the ejection head 50 in the main scanning direction X each
time the ejection head 50 is driven to move a fixed distance, or
the fine pitch p, in the sub-scanning direction Y. The ejection
nozzles of the ejection head 50 may be adapted to selectively eject
required ink upon reaching a predetermined ink ejection position
over the object 9 to achieve the printing on the object 9.
[0126] Thus, in the first mode of operation, it is not necessary to
transmit information about the travel distance L to the
sub-scanning direction driver 20. The driving system for moving the
ejection head 50 in the main scanning direction X and in the
sub-scanning direction Y is required only to perform a steady
driving operation. This simplifies a mechanism for controlling the
driving system.
[0127] The first mode of operation is effective when a plurality of
inclined surfaces having different inclination angles are arranged
in the main scanning direction X as viewed from a certain
sub-scanning position, particularly when the surface of the object
9 has a continuously curved shape and the like, for the reason to
be described below. When the ejection head 50 is in such a
sub-scanning position, the travel distance L for providing the
optimum dot-to-dot spacing is established for each of the inclined
surface. On some occasions, there is an inclined surface such that
the amount of movement of the ejection head 50 in the sub-scanning
direction is equal to the travel distance L established therefor,
after the ejection head 50 is driven to move the fine pitch p which
is the minimum unit of distance the ejection head 50 is driven in
the sub-scanning direction Y. Therefore, the movement of the
ejection head 50 at the fine pitch p and the driving of the
ejection head 50 in the main scanning direction X are alternately
repeated to allow stable printing on the object having a
three-dimensional complicated shape.
[0128] In the first mode of operation, however, there are occasions
when there is no such inclined surface that the amount of movement
of the ejection head 50 in the sub-scanning direction Y is equal to
the travel distance L established therefor, after the ejection head
50 is driven to move the fine pitch p in the sub-scanning direction
Y. On these occasions, the driving of the ejection head 50 in the
main scanning direction X at that sub-scanning position does not
involve the ejection of ink to become a factor responsible for the
reduction in printing efficiency.
[0129] A second mode of operation is effective to avoid such
reduction in printing efficiency.
[0130] The second mode of operation is such that the ejection head
50 is repeatedly driven to move the fine pitch p until the amount
of movement of the ejection head 50 in the sub-scanning direction Y
equals the travel distance L, and the ejection head 50 is not
driven in the main scanning direction X if the amount of movement
of the ejection head 50 in the sub-scanning direction Y does not
equal the travel distance L after the ejection head 50 is driven to
move the fine pitch p. In other words, the second mode of operation
is similar to the first mode in that the ejection head 50 is
repeatedly driven to move the fine pitch p in the sub-scanning
direction Y, but differs therefrom in that the ejection head 50 is
not moved in the main scanning direction X at a sub-scanning
position which does not involve the ejection of ink.
[0131] Thus, in the second mode of operation, the ejection head 50
is not driven in the main scanning direction X if ink ejection is
not involved. This saves the operating time, to reduce the time
required for printing, thereby increasing the printing efficiency
and achieving high-speed printing.
[0132] <A3. Ejection Pattern Control in Main Scanning Direction
X>
[0133] Next, ejection pattern control in the main scanning
direction X will be described. The ejection head 50 is moved
continuously, rather than stepwise, in the main scanning direction
X. Thus, the technique of providing a uniform dot distribution in
the main scanning direction X includes two methods: a method of
changing the velocity of the continuous movement of the ejection
head 50 in accordance with the inclined surface with respect to the
main scanning direction X; and a method of changing the timing of
ink ejection (i.e. the driving frequency of the ejection nozzles)
in accordance with the inclined surface while maintaining the
velocity of the continuous movement of the ejection head 50 at a
fixed value.
[0134] FIGS. 5A and 5B show the first method for ejection pattern
control in the main scanning direction X. FIG. 5A shows printing on
a horizontal surface in the main scanning direction X, and FIG. 5B
shows printing on an inclined surface at an inclination angle
.theta. with respect to the main scanning direction X.
[0135] In the example of operation shown in FIGS. 5A and 5B, the
travel velocity V of the ejection head 50 moving continuously in
the main scanning direction is changed in accordance with the
inclined surface with respect to the main scanning direction X.
[0136] More specifically, when ejecting ink onto the horizontal
surface in the main scanning direction X, the ejection head 50 is
moved at a main scanning velocity V, as shown in FIG. 5A. On the
other hand, when ejecting ink onto the inclined surface at the
inclination angle .theta. with respect to the main scanning
direction X, the travel velocity of the ejection head 50 is changed
to a main scanning velocity V cos .theta. depending on the
inclination angle .theta., as shown in FIG. 5B.
[0137] For instance, it is assumed that, for a uniform dot-to-dot
spacing d in the main scanning direction X on the horizontal
surface, the driving frequency for driving the ejection nozzles of
the ejection head 50 moving at the main scanning velocity V is set
at f (Hz), as shown in FIG. 5A. In order for the ejection head 50
to form a uniform dot distribution having the dot-to-dot spacing d
on the inclined surface at the inclination angle .theta., it is
necessary to change the travel velocity V of the ejection head 50
in the main scanning direction X in accordance with the inclination
angle .theta. when the driving frequency f (Hz) is maintained at a
fixed value. In the example of operation shown in FIG. 5B, even
when ejecting ink onto the inclined surface at the inclination
angle .theta. without changing the driving frequency f (Hz), the
ejection head 50 moving at the main scanning velocity
V.sub..theta.=V cos .theta. can provide the dot-to-dot spacing d on
the inclined surface which is equal to the dot-to-dot spacing d to
be formed on the horizontal surface, to achieve the uniform dot
distribution.
[0138] FIGS. 6A and 6B show the second method for ejection pattern
control in the main scanning direction X. FIG. 6A shows printing on
a horizontal surface in the main scanning direction X, and FIG. 6B
shows printing on an inclined surface at an inclination angle
.theta. with respect to the main scanning direction X.
[0139] In the example of operation shown in FIGS. 6A and 6B, the
timing of ejection of ink from the ejection nozzles, or the driving
frequency of the ejection nozzles, is changed in accordance with
the inclined surface with respect to the main scanning direction X,
while the travel velocity V of the ejection head 50 moving
continuously in the main scanning direction X is held constant.
[0140] More specifically, the travel velocity of the ejection head
50 moving continuously in the main scanning direction X, i.e. the
main scanning velocity, is held constant at V. When ejecting ink
onto the horizontal surface in the main scanning direction X, the
driving frequency of the ejection nozzles of the ejection head 50
is set at f, as shown in FIG. 6A. On the other hand, when ejecting
ink onto the inclined surface at the inclination angle .theta. with
respect to the main scanning direction X, the driving frequency
f.sub..theta. of the ejection nozzles of the ejection head 50 is
changed to f.sub..theta.=f/cos .theta. depending on the inclination
angle .theta., as shown in FIG. 6B.
[0141] For instance, it is assumed that, for a uniform dot-to-dot
spacing d in the main scanning direction X on the horizontal
surface, the driving frequency for driving the ejection nozzles of
the ejection head 50 moving at the main scanning velocity V is set
at f (Hz), as shown in FIG. 6A. In order for the ejection head 50
to form a uniform dot distribution having the dot-to-dot spacing d
on the inclined surface at the inclination angle .theta. while the
main scanning velocity V is held constant, it is necessary to
change the driving frequency f.sub..theta. in accordance with the
inclination angle .theta.. In the example of operation shown in
FIG. 6B, when ejecting ink onto the inclined surface at the
inclination angle .theta., the driving frequency f.sub..theta. of
the ejection nozzles is changed to f.sub..theta.=f/cos .theta. (Hz)
depending on the inclined surface at the inclination angle .theta.
while maintaining the main scanning velocity at V. This provides
the dot-to-dot spacing d on the inclined surface which is equal to
the dot-to-dot spacing d to be formed on the horizontal surface, to
achieve the uniform dot distribution.
[0142] As described above, since the ejection head 50 is moved
continuously, rather than stepwise, in the main scanning direction
X, the use of any one of the two abovementioned methods of
operation for the uniform dot distribution in the main
scanning-direction X allows the dot-to-dot spacing in the main
scanning direction X to be held uniform, independently of the
presence or absence of the inclination. Although only one of the
main scanning velocity V.sub..theta. and the driving frequency
f.sub..theta. is illustrated as changed in accordance with the
inclination angle .theta. in the above description, the present
invention is not limited to this, but may be controlled to change
both of the main scanning velocity V.sub..theta. and the driving
frequency f.sub..theta.. More specifically, a combination
(V.sub..theta., f.sub..theta.) of the main scanning velocity
V.sub..theta. and the driving frequency f.sub..theta. is not
limited to (V cos .theta., f) and (V, f/cos .theta.), but may be
other combinations (V.sub..theta., f.sub..theta.) which satisfy the
relationship: V.sub..theta./f.sub..theta.=V cos .theta./f.
[0143] <A4. Control Mechanism and Overall Operation in Printing
Apparatus 100A>
[0144] A control mechanism in the printing apparatus 100A will be
described hereinafter.
[0145] FIG. 7 is a block diagram of the control mechanism in the
printing apparatus 100A. As illustrated in FIG. 7, the printing
apparatus 100A comprises an image data receiver 41, a shape data
receiver 42, the controller 43, a RAM 44, a ROM 45, the main
scanning direction driver 10, the sub-scanning direction driver 20,
the ejection head rotation driver 30, various sensors 47, and the
ejection nozzle driver 60. The image data receiver 41 receives from
an externally connected host computer CP image data about what is
to be printed on the object 9 which is represented as an image. The
shape data receiver 42 receives from the host computer CP shape
data about the shape of the surface of the object 9. Hence, the
surface shape of the three-dimensional object is recognized.
[0146] The controller 43 determines the ejection patterns of the
printing ink to be ejected in the main scanning direction X and in
the sub-scanning direction Y, respectively, for printing on the
object 9, and controls the main scanning direction driver 10, the
sub-scanning direction driver 20, the ejection nozzle driver 60 and
the like based on the determined ejection patterns, thereby to
achieve the uniform dot distribution on the object 9. The RAM 44 is
a memory for storing the image data and the shape data both
received from the host computer CP, and data about the respective
ejection patterns for controlling the printing operation, such as
data about the travel distance L in the sub-scanning direction Y.
The ROM 45 is a memory for storing a program corresponding to a
printing procedure (the flowchart of FIG. 8 to be described later)
to be executed by the controller 43.
[0147] The main scanning direction driver 10 provided inside the
rail RL (See FIG. 1) drives a predetermined motor and the like
based on an operating instruction from the controller 43 to move
the head holding mechanism 13 along the rail RL, thereby moving the
ejection head 50 in the main scanning direction X.
[0148] The sub-scanning direction driver 20 provided in the base
plate 81 (See FIG. 1) drives a predetermined motor and the like
based on an operating instruction from the controller 43 to move
the stands ST along the grooves 83 extending in the Y direction,
thereby moving the ejection head 50 in the sub-scanning direction
Y.
[0149] The ejection head rotation driver 30 provided in the head
holding mechanism 13 rotates the ejection head 50 within an X-Y
plane based on an operating instruction from the controller 43.
This rotational operation is particularly effective when the
ejection head 50 has a multi-nozzle form, which will be described
later.
[0150] The various sensors 47 are sensing means for sensing the
home position of each operating mechanism component such as the
main scanning direction driver 10, and for detecting the amount of
ink remaining in the ejection head 50 and the like. This sensing
means achieves correct operation in each direction and allows a
user to know the time to replace an ink tank and the like.
[0151] The ejection nozzle driver 60 provided in the ejection head
50 causes the ejection nozzles of the ejection head 50 to eject
ink, based on the ejection timing from the controller 43.
[0152] Description will be given on the operation for printing on
the three-dimensional object 9 in practice in the printing
apparatus 100A having the above-mentioned construction.
[0153] FIG. 8 is a flowchart showing the overall operation of the
printing apparatus 100A. The flowchart of FIG. 8 illustrates the
procedure principally executed in the controller 43 in the printing
apparatus 100A.
[0154] First, in Step S11, the surface of the object 9 to be
printed is approximated by n polygonal faces (where n is an
integer). That is, the surface shape of the three-dimensional
object is approximated by a polyhedron comprised of a plurality of
polygons. More specifically, upon receiving the shape data about
the object 9 from the host computer CP, the controller 43 processes
the data, even if the object 9 has a surface shape including smooth
projections and depressions or the like, to represent the surface
shape as a set of polygonal faces.
[0155] FIGS. 9A, 9B, 10A, 10B, 11A and 11B show examples of the
approximation of the shape of the object 9 which is made by
polygonal faces in the controller 43. FIGS. 9A and 9B show the
object 9 to be subjected to printing which is inclined with respect
to only the main scanning direction X, FIGS. 10A and 10B show the
object 9 to be subjected to printing which is inclined with respect
to only the sub-scanning direction Y, and FIGS. 11A and 11B show
the object 9 to be subjected to printing which is inclined with
respect to both the main scanning direction X and the sub-scanning
direction Y.
[0156] In the case shown in FIGS. 9A and 9B, the shape data about
the object 9 given from the host computer CP includes a surface
smoothly curved with respect to the main scanning direction X, as
shown in FIG. 9A. In this state, however, since the inclination
angle of the object 9 changes continuously with respect to the main
scanning direction X, it is necessary to determine the inclination
angles at all ink striking positions with respect to the main
scanning direction X and accordingly to produce the ejection
pattern for each of the ink striking positions. This requires
enormous calculations. To solve this problem, the controller 43
segments the surface shape of the object 9 into a plurality of
regions arranged in the main scanning direction X, as shown in FIG.
9B, to approximate the curved face of each of the regions by a
planar polygonal face. Consequently, the curved surface with
respect to the main scanning direction X is represented by the
plurality of polygonal faces. The controller 43 determines the
inclination angle with respect to the main scanning direction X for
each of the polygons, to change the ejection pattern.
[0157] In the case shown in FIGS. 10A and 10B, the shape data about
the object 9 given from the host computer CP includes a surface
smoothly curved with respect to the sub-scanning direction Y, as
shown in FIG. 10A. In this state, however, since the inclination
angle of the object 9 changes continuously with respect to the
sub-scanning direction Y, it is necessary to determine the
inclination angles at all ink striking positions with respect to
the sub-scanning direction Y and accordingly to produce the
ejection pattern for each of the ink striking positions. This
requires enormous calculations. To solve this problem, the
controller 43 segments the surface shape of the object 9 into a
plurality of regions arranged in the sub-scanning direction Y, as
shown in FIG. 10B, to approximate the curved face of each of the
regions by a planar polygonal face. Consequently, the curved
surface with respect to the sub-scanning direction Y is represented
by the plurality of polygonal faces. The controller 43 determines
the inclination angle with respect to the sub-scanning direction Y
for each of the polygons, to change the ejection pattern.
[0158] In the case shown in FIGS. 11A and 11B, the shape data about
the object 9 given from the host computer CP includes a surface
smoothly curved with respect to both the main scanning direction X
and the sub-scanning direction Y, as shown in FIG. 11A. In this
state, however, since the inclination angle of the object 9 changes
continuously with respect to both the main scanning direction X and
the sub-scanning direction Y, it is necessary to determine the
inclination angles at all ink striking positions with respect to
both the main scanning direction X and the sub-scanning direction Y
and accordingly to produce the ejection pattern for each of the ink
striking positions. This requires enormous calculations. To solve
this problem, the controller 43 segments the surface shape of the
object 9 into a plurality of regions, as shown in FIG. 11B, to
approximate the curved face of each of the regions by a planar
polygonal face. Consequently, the curved surface of the object 9 is
represented by the plurality of polygonal faces. The controller 43
determines the inclination angles with respect to both the main
scanning direction X and the sub-scanning direction Y for each of
the polygons, to change the ejection pattern.
[0159] The approximation is made by the n polygonal faces in this
manner in Step S11. Such polygonal approximation can improve the
printing efficiency. The use of the polygonal approximation
requires the controller 43 only to determine the printing
conditions and the like for each polygon with respect to the main
scanning direction X and the sub-scanning direction Y and to change
the printing operation for each polygon. Thus, the use of n
polygons requires the change in ejection pattern for printing
operation to be made n times.
[0160] It is possible to change the ejection pattern each time the
inclination angle of the continuously changing curved surface is
determined for each position of the ejection head without making
the polygonal approximation. However, this process necessitates the
change in ejection pattern each time a droplet of ink is ejected,
to cause significantly complicated control for printing operation
and require enormous time for arithmetic and printing
operations.
[0161] The use of the polygonal approximation of the object surface
allows the printing operation to be performed under the same
condition for each polygon, to achieve efficient printing.
[0162] Next, in Step S12, a polygon parameter i is initialized to
"1." In Step S13, the inclination angle .theta.x of the i-th
polygon with respect to the main scanning direction X is
determined. In Step S14, the driving condition in the main scanning
direction X is determined in accordance with the inclination angle
.theta.x, and the determined driving condition is temporarily
stored in the RAM 44. As stated above, the determined driving
condition includes the ejection frequency (f/cos .theta. x) and/or
the driving velocity (V.times.cos .theta. x). In Step S15, the
polygon parameter i is incremented by one, and the flow proceeds to
Step S16. In Step S16, a judgement is made as to whether or not the
driving condition in the main scanning direction X has been
determined for all of the n polygons. If the determination for all
of the n polygons is completed, the flow proceeds to Step S17. If
the determination for all of the n polygons is not completed, the
flow returns to Step S13 to determine the driving condition for the
next polygon.
[0163] The processes in Steps S12 to S16 are performed to determine
the driving condition in the main scanning direction X for all
polygons. After the driving condition in the main scanning
direction X is determined for all polygons, processes in Steps S17
to S22 are then executed to determine the driving condition in the
sub-scanning direction Y (i.e. the stepwise travel distance L in
the sub-scanning direction Y).
[0164] In Step S17, the polygon parameter i is initialized to "1."
In Step S18, the inclination angle .theta.y of the i-th polygon
with respect to the sub-scanning direction Y is determined. Then,
in Step S19, an integer k which minimizes the absolute value of
(cos .theta.y-k/10) is determined. The integer k is a value
indicating the cumulative value of the fine pitch p in the
sub-scanning direction Y. In Step S20, the travel distance L in the
sub-scanning direction Y for providing the dot-to-dot spacing
equaling d for the i-th polygon is set at k.times.d/10. In other
words, when the travel distance L=k.times.d/10 for the i-th
polygon, the dot-to-dot spacing in the sub-scanning direction is
closest to the dot-to-dot spacing d on the horizontal surface. The
travel distance L determined in Step S20 is temporarily stored in
the RAM 44. In Step S21, the polygon parameter i is incremented by
one, and the flow proceeds to Step S22. In Step S22, a judgement is
made as to whether or not the travel distance L in the sub-scanning
direction Y has been determined for all of the n polygons. If the
determination for all of the n polygons is completed, the flow
proceeds to Step S23. If the determination for all of the n
polygons is not completed, the flow returns to Step S18 to
determine the travel distance L for the next polygon.
[0165] Next, processes in Steps S23 to S26 are executed for
printing on each of the polygons.
[0166] In Step S23, the polygon parameter i is initialized to "1."
In step S24, the controller 43 obtains from the RAM 44 the driving
condition in the main scanning direction X and the travel distance
in the sub-scanning direction Y for the i-th polygon, to perform
printing on an i-th target region surface (the actual surface
approximated by the i-th polygon) based on the obtained data. After
the printing operation on that region surface, the polygon
parameter i is incremented by one in Step S25, and the flow
proceeds to Step S26. In Step S26, a judgement is made as to
whether or not the printing operation has been completed for all of
the n polygons. If the printing operation for all of the n polygons
is completed, the printing operation on the object 9 is terminated.
If the printing operation for all of the n polygons is not
completed, the flow returns to Step S24 to start the printing
operation for the next polygon.
[0167] In the printing operation in Step S24, the ejection head 50
is driven in the main scanning direction X based on the driving
condition determined for each polygon, and is moved stepwise in the
sub-scanning direction Y based on the travel distance L determined
for each polygon. Therefore, the printing operation in Step S24
allows the plurality of polygons to be substantially identical in
dot-to-dot spacing both in the main scanning direction X and in the
sub-scanning direction Y, to form the uniform dot distribution.
[0168] <A5. Multi-Nozzle Form of Ejection Head>
[0169] Description is given on a multi-nozzle arrangement of the
ejection head 50 including a plurality of ejection nozzles for
ejecting the printing ink. The multi-nozzle arrangement of the
ejection head 50 produces the peculiar function and effect of
simultaneously ejecting a plurality of ink droplets to achieve
high-speed printing.
[0170] When the plurality of ejection nozzles are arranged in the
sub-scanning direction Y, the spacings between the nozzles are
constant in the sub-scanning direction Y. The ink ejected from the
constantly spaced ejection nozzles produces dots between which gaps
are formed depending on the constant spacings. It is therefore
necessary to fill the gaps with dots by repeatedly driving the
ejection nozzles in the sub-scanning direction Y.
[0171] For printing on the horizontal surface, the travel distance
L in the sub-scanning direction Y may be set at the distance d
which provides the dense dot distribution (See FIG. 4A), thereby to
fill the gaps with the dots evenly and properly.
[0172] However, for printing on an inclined surface, since the
travel distance L in the sub-scanning direction Y is set at a
distance which provides the dense dot distribution (See FIGS. 4B to
4D), the gaps between the dots resulting from the constant spacing
between the ejection nozzles are not filled with the dots evenly
and properly.
[0173] To avoid this phenomenon, it is desirable to change the
spacing between the ejection nozzles in accordance with the
inclination with respect to the sub-scanning direction Y. It is,
however, technically difficult to freely change the spacing between
the ejection nozzles of the ejection head 50.
[0174] The printing apparatus 100A is designed to rotate the
ejection head 50 by the ejection head rotation driver 30 in
accordance with the inclination angle with respect to the
sub-scanning direction Y to control the spacing between the
ejection nozzles in the sub-scanning direction.
[0175] FIG. 12 shows the rotational operation of the ejection head
50. As shown in FIG. 12, the ejection head 50 is adapted to rotate
within the X-Y plane as the ejection head rotation driver 30
rotates the rotary shaft AR. Consequently, when the plurality of
ejection nozzles are arranged in the sub-scanning direction Y on
the underside of the ejection head 50, this structure can control
the nozzle-to-nozzle spacing in the sub-scanning direction Y.
[0176] Three examples of the multi-nozzle arrangement of the
ejection head 50 will be specifically described with reference to
FIGS. 13A, 13B, 13C, 14A, 14B, 14C, 15A, 15B and 15C. For
multi-color printing on the object 9, the ejection head 50 of the
multi-nozzle arrangement to be described below comprises the
plurality of ejection nozzles for each of the four color
components: Y (yellow), M (magenta), C (cyan) and K (black).
[0177] FIGS. 13A, 13B and 13C show a first example of the
multi-nozzle arrangement including a plurality of ejection nozzles
52 for the color components Y, M, C and K arranged in a column in
the sub-scanning direction Y.
[0178] FIG. 13A shows the nozzle unit 51 of the ejection head 50 as
viewed from the object 9. As shown in FIG. 13A, the nozzle unit 51
includes an array of ejection nozzles 52 for each color component
Y, M, C and K which are arranged in a column in the sub-scanning
direction Y, with the nozzle arrays for the respective color
components arranged in a column.
[0179] For printing by such an ejection head 50 on the inclined
surface at the inclination angle .theta. with respect to the
sub-scanning direction Y, the travel distance L of the ejection
head 50 in the sub-scanning direction Y is determined in accordance
with the inclination angle .theta. in the above-mentioned manner,
and a rotation angle .theta. is imparted to the ejection head 50 to
rotate the nozzle unit 51 in accordance with the inclination angle
.theta., as shown in FIG. 13B. Consequently, the column of the
ejection nozzles 52 arranged in the sub-scanning direction Y before
the rotation forms an angle .theta. with the sub-scanning direction
Y after the rotation.
[0180] FIG. 13C is an enlarged view of a portion A (or an ejection
nozzle portion) shown in FIG. 13B. The rotation of the nozzle unit
51 in accordance with the inclination angle .theta. with respect to
the sub-scanning direction Y provides a nozzle-to-nozzle spacing in
the sub-scanning direction Y which equals r cos .theta. where r is
a physical distance between adjacent nozzles in the nozzle unit 51.
This substantially reduces the spacing between the ejection nozzles
in the sub-scanning direction Y.
[0181] Thus imparting the rotation angle equaling the inclination
angle .theta. of the inclined surface to the ejection head 50
allows the spacing between the dots formed by the ink ejected from
adjacent ejection nozzles 52 to be maintained at r on the inclined
surface. This dot-to-dot spacing r is equal to the spacing between
the dots formed by the adjacent ejection nozzles 52 in the case of
printing on the horizontal surface by the multi-nozzle arrangement.
Therefore, the printing operation by setting the travel distance L
of the ejection head 50 in the sub-scanning direction Y so as to
provide a dot distribution similar to that on the horizontal
surface can form the dots in the gaps of the dot-to-dot spacing r
evenly and properly as the ejection head 50 moves in the
sub-scanning direction Y.
[0182] Even if the travel distance L of the ejection head 50 in the
sub-scanning direction Y in accordance with the inclination angle
.theta. is set to be smaller than that in the case of printing on
the horizontal surface, the nozzle-to-nozzle spacing in the
sub-scanning direction Y becomes accordingly smaller. Thus, the
gaps between the dots of ink ejected from the plurality of ejection
nozzles 52 are filled with the dots evenly and properly.
Consequently, high-definition printing is achieved.
[0183] In this case, however, the rotation of the ejection head 50
changes the positional relationship of the ejection nozzles 52
relative to the main scanning direction X. Therefore, when the
controller 43 generates data for the printing operation (more
specifically, the data representing the timing of driving of the
ejection nozzles), it is necessary to previously consider the
change in position of the ejection nozzles 52 relative to the main
scanning direction X to generate corrected data about the position
change.
[0184] FIGS. 14A, 14B and 14C show a second example of the
multi-nozzle arrangement in which an array of ejection nozzles 52
for each color component Y, M, C and K are arranged in a column in
the sub-scanning direction Y, and the nozzle arrays for the
respective color components are arranged in parallel.
[0185] FIG. 14A shows the nozzle unit 51 of the ejection head 50 as
viewed from the object 9. As shown in FIG. 14A, the nozzle unit 51
includes the array of ejection nozzles 52 for each color component
Y, M, C and K which are arranged in a column in the sub-scanning
direction Y, with the nozzle arrays for the respective color
components arranged in parallel with the Y direction.
[0186] For printing by such an ejection head 50 on the inclined
surface at the inclination angle .theta. with respect to the
sub-scanning direction Y, the travel distance L of the ejection
head 50 in the sub-scanning direction Y is determined in accordance
with the inclination angle .theta. in the above-mentioned manner,
and the rotation angle .theta. is imparted to the ejection head 50
to rotate the nozzle unit 51 in accordance with the inclination
angle .theta., as shown in FIG. 14B. Consequently, the column, for
each color component, of the ejection nozzles 52 arranged in the
sub-scanning direction Y before the rotation forms the angle
.theta. with the sub-scanning direction Y after the rotation.
[0187] FIG. 14C is an enlarged view of the portion A (or the
ejection nozzle portion) shown in FIG. 14B. The rotation of the
nozzle unit 51 in accordance with the inclination angle .theta.
with respect to the sub-scanning direction Y provides a
nozzle-to-nozzle spacing in the sub-scanning direction Y which
equals r cos .theta. where r is the physical distance between
adjacent nozzles for the same color component in the nozzle unit
51. This substantially reduces the spacing between the ejection
nozzles in the sub-scanning direction Y.
[0188] Thus imparting the rotation angle equaling the inclination
angle .theta. of the inclined surface to the ejection head 50
allows the spacing between the dots formed by the ink ejected from
adjacent ejection nozzles 52 to be maintained at r on the inclined
surface. This dot-to-dot spacing r is equal to the spacing between
the dots formed by the adjacent ejection nozzles 52 in the case of
printing on the horizontal surface by the multi-nozzle arrangement.
Therefore, the printing operation by setting the travel distance L
of the ejection head 50 in the sub-scanning direction Y so as to
provide a dot distribution similar to that on the horizontal
surface can form the dots in the gaps of the dot-to-dot spacing r
evenly and properly as the ejection head 50 moves in the
sub-scanning direction Y.
[0189] However, this is based on the consideration focused on the
same color component, and causes an unpreferable relationship with
other color components. More specifically, the rotation of the
nozzle unit 51 through the angle .theta. causes a K ejection nozzle
52a and a C ejection nozzle 52b both of which would otherwise scan
the same sub-scanning position to differ in sub-scanning position
from each other to create a deviation corresponding to a distance
e. Therefore, this multi-nozzle arrangement requires printing
control for each color component, for example, in such a manner
that the printing operation for K is initiated to move the ejection
head 50 the distance e in the sub-scanning direction Y and then the
printing operation for C is initiated. This involves the problem of
the reduction in printing efficiency.
[0190] With this multi-nozzle arrangement, the change in position
of the ejection nozzles 52 relative to the main scanning direction
X also occurs. Therefore, it is necessary to previously generate
corrected data about the position change in the main scanning
direction X as described above.
[0191] FIGS. 15A, 15B and 15C show a third example of the
multi-nozzle arrangement including nozzle array members 51y, 51m,
51c and 51k for the respective color components Y, M, C and K, the
nozzle array members 51y, 51m, 51c and 51k being coupled together
by a pair of linkage mechanisms 54.
[0192] FIG. 15A shows the nozzle unit 51 of the ejection head 50 as
viewed from the object 9. As shown in FIG. 15A, the nozzle unit 51
comprises the nozzle array members 51y, 51m, 51c and 51k for the
respective color components Y, M, C and K each of which has the
array of ejection nozzles 52 arranged in a column in the
sub-scanning direction Y, and the pair of linkage mechanisms 54 for
coupling the nozzle array members 51y, 51m, 51c and 51k together at
their opposite ends as viewed in the sub-scanning direction. The
linkage mechanisms 54 are designed to prevent the deviation of the
positional relationship between the corresponding ejection nozzles
52 for the respective color components in the sub-scanning
direction Y when the ejection head rotation driver 30 drives the
ejection head 50 to rotate.
[0193] For printing by the ejection head 50 having such a nozzle
unit 51 on the inclined surface at the inclination angle .theta.
with respect to the sub-scanning direction Y, the travel distance L
of the ejection head 50 in the sub-scanning direction Y is
determined in accordance with the inclination angle .theta. in the
above-mentioned manner, and the rotation angle .theta. is imparted
to the ejection head 50.
[0194] FIG. 15B shows the nozzle unit 51 to which the rotation
angle .theta. is imparted. As shown in FIG. 15B, when the rotation
angle .theta. is imparted to the nozzle unit 51 in accordance with
the inclination angle .theta., the linkage mechanisms 54 act to
rotate the nozzle array members 51y, 51m, 51c and 51k through the
angle .theta.. Consequently, the column of the ejection nozzles 52
arranged in the sub-scanning direction Y in each of the nozzle
array members 51y, 51 m, 51c and 51k before the rotation forms the
angle .theta. with the sub-scanning direction Y after the
rotation.
[0195] FIG. 15C is an enlarged view of the portion A (or the
ejection nozzle portion) shown in FIG. 15B. The rotation of the
nozzle unit 51 in accordance with the inclination angle .theta.
with respect to the sub-scanning direction Y provides a
nozzle-to-nozzle spacing in the sub-scanning direction Y which
equals r cos .theta. where r is the physical distance between
adjacent nozzles for the same color component in the nozzle unit
51. This substantially reduces the spacing between the ejection
nozzles in the sub-scanning direction Y.
[0196] Thus imparting the rotation angle equaling the inclination
angle .theta. of the inclined surface to the ejection head 50
allows the spacing between the dots formed by the ink ejected from
adjacent ejection nozzles 52 to be maintained at r on the inclined
surface. This dot-to-dot spacing r is equal to the spacing between
the dots formed by the adjacent ejection nozzles 52 in the case of
printing on the horizontal surface by the multi-nozzle arrangement.
Therefore, the printing operation by setting the travel distance L
of the ejection head 50 in the sub-scanning direction Y so as to
provide a dot distribution similar to that on the horizontal
surface can form the dots in the gaps of the dot-to-dot spacing r
evenly and properly as the ejection head 50 moves in the
sub-scanning direction Y.
[0197] Additionally, the function of the linkage mechanisms 54
prevents the positional deviation of the corresponding ejection
nozzles in the nozzle array members 51y, 51m, 51c and 51k in the
sub-scanning direction Y.
[0198] As illustrated in FIGS. 15A, 15B and 15C, the nozzle unit 51
is divided into the nozzle array members 51y, 51m, 51c and 51k in
corresponding relation to the ejection nozzle arrays for the
respective color components, and the nozzle array members 51y, 51m,
51c and 51k are coupled together by the linkage mechanisms 54. This
arrangement can prevent the positional deviation of the
corresponding ejection nozzles for the respective color components
in the sub-scanning direction Y, and also can adjust the spacing
between adjacent ejection nozzles 52 in the sub-scanning direction
Y, to easily provide four-color simultaneous printing during one
main scanning operation, thereby achieving printing on the
three-dimensional object 9 most efficiently.
[0199] With this multi-nozzle arrangement, the change in position
of the ejection nozzles 52 relative to the main scanning direction
X also occurs. Therefore, it is necessary to previously generate
corrected data about the position change in the main scanning
direction X as described above.
[0200] <B. Second Preferred Embodiment>
[0201] <B1. Construction of Printing Apparatus>
[0202] <Overall Construction>
[0203] FIG. 16 is a perspective view of a three-dimensional object
printing apparatus 100B (also referred to simply as a "printing
apparatus" hereinafter) according to a second preferred embodiment
of the present invention. The printing apparatus 100B is an
apparatus for printing on a three-dimensional object. The
construction of the printing apparatus 100B will be described with
reference to FIG. 16. Three mutually orthogonal axes (X, Y and Z
axes) are defined as those depicted in FIG. 16 herein.
[0204] The printing apparatus 100B comprises an ink ejection
section 1, a shape measuring section 2, a scanning section 3, a
control section 5, and an external input/output section 6 (See FIG.
18). These sections will be discussed below.
[0205] <Scanning Section>
[0206] The scanning section 3 moves the ink ejection section 1
relative to an object 7. More specifically, the scanning section 3
comprises a plurality of scanning sections corresponding to
respective axial directions, i.e., an X-direction scanning section
31, a Y-direction scanning section 32, a Z-direction scanning
section 33, and an R-direction scanning section 34.
[0207] In the printing apparatus 100B, the Y-direction scanning
section 32 is contained in a table TB, and moves the R-direction
scanning section 34 mounted to an output portion of the Y-direction
scanning section 32 linearly in the Y direction. The object 7 is
fixed to a turntable 341 serving as an output portion of the
R-direction scanning section 34. A three-dimensional object of a
pyramidal configuration is illustrated in FIG. 16 as an example of
the object 7. A suitable method of fixing the object 7 to the
turntable 341 may be used depending on the shape of the object 7.
Examples of the fixing method include a method of holding the
object 7 at its opposite ends in a manner like a vice, a method of
pressing a non-printing portion of the object 7 against the
turntable 341 with a spring retainer, and a method of bonding the
object 7 to the turntable 341 with an adhesive tape or the like,
for example, in the case where the object 7 has a relatively large
contact area with the turntable 341 as illustrated. The object 7 is
fixed on the turntable 341 by these retaining mechanisms, and is
rotated in the R direction, or about the Z axis, by the R-direction
scanning section 34.
[0208] The printing apparatus 100B further comprises a pair of
stands SD extending vertically from the table TB placed
horizontally on the floor. Each of the pair of stands SD has a
first end mounted on the table TB, and a second end supporting the
X-direction scanning section 31, as illustrated in FIG. 16. The
X-direction scanning section 31 has an output portion for holding
the Z-direction scanning section 33, and moves the Z-direction
scanning section 33 linearly in the X direction. The Z-direction
scanning section 33 has an output shaft 331 to which are mounted
the ink ejection section 1 and the shape measuring section 2
integral with each other to form a print head section H, and moves
the print head section H linearly in the Z direction.
[0209] Thus, the printing apparatus 100B has the plurality of
scanning sections corresponding to the respective directions (X, Y,
Z and R directions), i.e., the X-direction scanning section 31, the
Y-direction scanning section 32, the Z-direction scanning section
33, and the R-direction scanning section 34. A combination of these
scanning sections 31, 32, 33 and 34 corresponding to the respective
directions allows the ink ejection section 1 and the shape
measuring section 2 to move relative to the object 7 in a
three-dimensional space. The printing apparatus 100B further
comprises a cover CV indicated by the broken lines in FIG. 16 on
the outer periphery thereof for covering the printing apparatus
100B during printing to prevent ink from scattering outwardly and
to prevent a user from contacting the driving sections.
[0210] <Ink Ejection Section>
[0211] FIG. 17 shows the print head section H (H1) mounted to the
output shaft 331 of the Z-direction scanning section 33 as viewed
obliquely from below. The print head section H has the ink ejection
section 1 and the shape measuring section 2 disposed integrally
together. These sections will be described one by one with
reference to FIG. 17.
[0212] As illustrated in FIG. 17, the ink ejection section 1
comprises an ink ejection head section 11 and an ink reservoir
12.
[0213] The ink ejection head section 11 comprises a C ink ejection
head section 111 for ejecting C (cyan) ink, an M ink ejection head
section 112 for ejecting M (magenta) ink, a Y ink ejection head
section 113 for ejecting Y (yellow) ink, and a K ink ejection head
section 114 for ejecting K (black) ink. The four ink ejection head
sections 111, 112, 113 and 114 for the respective colors (C, M, Y
and K) comprise a plurality of C (cyan) ink ejection nozzles 111N,
a plurality of M (magenta) ink ejection nozzles 112N, a plurality
of Y (yellow) ink ejection nozzles 113N, and a plurality of K
(black) ink ejection nozzles 114N, respectively, for ejecting the
inks of the corresponding colors (C, M, Y and K). These nozzles are
shown as arranged in a linear array for each of the four colors. It
is assumed that the ink ejection nozzles 111N to 114N used herein
are of an ink jet type.
[0214] The ink reservoir 12 comprises a C ink reservoir 121, an M
ink reservoir 122, a Y ink reservoir 123, and a K ink reservoir 124
(See FIG. 18). These ink reservoirs 121, 122, 123 and 124 for the
respective colors not shown in FIGS. 16 and 17 are contained in the
ink reservoir 12.
[0215] The C, M, Y and K ink ejection nozzles 111N to 114N are
supplied with the four color inks from the C, M, Y and K ink
reservoirs 121 to 124, respectively, to selectively eject the inks
toward the object 7. This provides printing (coloring) on the
surface of the object 7.
[0216] The types of the inks to be used are not limited to those
described above. The inks required to color the surface of the
object 7 are properly combined depending on the colors and
characteristics of the inks. For multi-color printing, it is
necessary to provide a plurality of ink ejection head sections for
different color inks depending on required colors, and an equal
plurality of ink reservoir tanks for storing the respective color
inks. For example, the four colors C, M, Y and K may be used singly
or in combination, or a combination of R (red), G (green) and B
(blue) may be used. Alternatively, a mixture of these color inks or
an ink mixed with a luster pigment or the like may be used. The
number of inks to be selected among these inks may be increased or
decreased, as required, or the sequence of the application of the
inks may be changed. For single-color printing (in the case where
the ink to be used is of a single color), it is necessary to
provide only at least one ink ejection nozzle and at least one ink
reservoir tank.
[0217] A multi-nozzle arrangement illustrated in FIG. 17 is such
that the plurality of ink ejection nozzles 111N to 114N are
arranged in a linear array for each color. However, since a smaller
head section which can be moved closer to the object is
advantageous particularly when the object has a greater inclination
or a rougher surface, the number of nozzles may be reduced or a
single-nozzle arrangement may be used. However, the decrease in the
number of nozzles (or the use of the single-nozzle arrangement)
requires longer printing time than the use of a multi-nozzle
arrangement including more nozzles. It is therefore preferable to
give a higher priority to the reduction in printing time and to use
the multi-nozzle arrangement (particularly the multi-nozzle
arrangement including a multiplicity of nozzles) when the object 7
has a less rough surface.
[0218] Although assumed to be of the ink jet type, the ink ejection
nozzles 111N, 112N, 113N and 114N may be of a spray gun type,
depending on the characteristic of a required image. Alternatively,
the printing apparatus 100B may comprise both ink jet type ejection
nozzles and spray gun type ejection nozzles to select between ink
ejection from the ink jet type ejection nozzles and ink ejection
from the spray gun type ejection nozzles so that the ink jet type
ejection nozzles are used to print on a confined area or an area in
which a high-definition image is required whereas the spray gun
type ejection nozzles are used to coat a wide area with ink in a
short time or to print on an area in which moderate blurriness is
required.
[0219] The ink ejection head section 11 including the ink ejection
nozzles and the ink reservoir 12 are shown in FIGS. 16 and 17 as
provided integrally in the print head section H, but need not
necessarily be integral with each other. It is desirable that the
ink ejection nozzles are arranged as close as possible to each
other since this arrangement can reduce the head size to make the
ink ejection head section 11 easy to approach the object. On the
other hand, the ink reservoir 12 may be designed so that C, M, Y
and K ink reservoirs 121 to 124 are provided separately from each
other. For increase in ink storage capacity of the ink reservoir 12
or for reduction in the entire mounting area thereof to the output
shaft 331, the C, M, Y and K ink reservoirs 121 to 124 may be
provided in the body of the Z-direction scanning section 33, with
flow channels provided between the ink reservoirs 121 to 124 and
the ink ejection nozzles.
[0220] <Shape Measuring Section>
[0221] Next, the shape measuring section 2 will be described. The
shape measuring section 2 described herein is assumed to comprise
an optical displacement sensor 2A. The optical displacement sensor
2A of the shape measuring section 2 includes a phototransmitter 21
and a photoreceiver 22. The phototransmitter 21 directs laser light
downwardly in the Z direction, and the photoreceiver 22 including a
line sensor (CCD, PSD (optical position detecting device) or the
like) and a lens receives light diffuse-reflected from the surface
of the object 7. Thus, the optical displacement sensor 2A can
measure a distance by a triangulation technique. Hence, the surface
shape of the three-dimensional object is recognized.
[0222] It is assumed herein that a predetermined plane (for
example, the plane Z=0) parallel to the X-Y plane is used as a
reference plane of measurement and a distance is measured in the Z
direction at each point (X, Y). More specifically, the displacement
sensor 2A measures a distance from each point (X, Y) within the
reference plane to the surface of the object 7 in a direction (Z
direction) perpendicular to the reference plane, thereby to measure
the shape of the surface of the object 7. The reference plane is
also perpendicular to the direction (Z direction) in which the ink
ejection section 1 ejects ink. The scanning section 3 is capable of
scanning in two directions (X direction and Y direction) parallel
to the reference plane.
[0223] The shape measuring section 2 is disposed integrally with
the ink ejection section 1 in the print head section H, and scans
the surface of the object 7 simultaneously with the scanning of the
scanning section 3. This eliminates the need for a separate driving
mechanism to increase efficiency. Further, the ink ejection section
1 and the shape measuring section 2 are operated simultaneously by
the same scanning operation of the scanning section 3, as will be
described later, to achieve more efficient measuring and printing
operations.
[0224] The shape measuring section 2 includes, but is not limited
to, the reflective optical sensor. Other optical sensors, contact
sensors or ultrasonic sensors may be used. However, the distance
information detected by these sensors is obtained as an average
value within the area subjected to the distance measurement (for
example, the area of a spot irradiated with the laser light in the
case of the optical sensor). Then, the resultant three-dimensional
shape data is blurred as if it were filtered by a low pass filter.
It is therefore preferable to use a sensor capable of measuring a
distance within a small area (e.g., as small as the area of a dot
formed when ink strikes the surface of the object) in order to
detect edges or finely rugged shapes more correctly.
[0225] <Control Section>
[0226] The control section 5 will be described with reference to
the diagram of FIG. 18. The control section 5, not shown in FIG.
16, is provided inside or separately outside the body of the
printing apparatus 100B.
[0227] The control section 5 comprises an ink ejection controller
511, an ink ejection control driver 512, a shape measurement
controller 521, a shape measurement control driver 522, a scanning
controller 531, a scanning control driver 532, a CPU 53, a
semiconductor memory (also referred to simply as a "memory"
hereinafter) 55 such as a ROM and a RAM, and an auxiliary storage
56 (hard disk drive).
[0228] In the memory 55 and/or the auxiliary storage 56 is stored a
software program (also referred to simply as a "program"
hereinafter) for controlling the driving of the sections 1, 2 and
3, i.e., for controlling the ejection timing of the color inks from
the ink ejection section 1, the operation of measurement of the
shape measuring section 2 and the scanning of the scanning section
3. Also stored in the memory 55 and/or the auxiliary storage 56 are
a program for creating three-dimensional shape data from the
distance information obtained by the shape measuring section 2, a
program for associating image data with the three-dimensional shape
data, a program for planning a printing procedure based on these
data, and required data including a geometrical position correction
table for the ink ejection nozzles and the shape measuring section
2, a scanning velocity correction table, and an ink ejection timing
correction table.
[0229] The CPU 53 executes a program containing procedures
corresponding to different image formation procedures to be
described later to perform sequential processing based on the data
stored in the memory 55, thereby outputting control signals to the
controllers 511, 521 and 531. The controllers 511, 521 and 531
process the control signals to transmit to the drivers 512, 522 and
532 signals for actually driving the ink ejection section 1, the
shape measuring section 2 and the scanning section 3, respectively.
In response to these signals, the drivers 512, 522 and 532 drive
the respective sections 1, 2 and 3.
[0230] The sections 1, 2 and 3 transmit signals through the drivers
512, 522 and 532 to the controllers 511, 521 and 531, as required,
respectively. In response to these signals, the CPU 53 feeds back
new control signals to the controllers 511, 521 and 531 based on
the data stored in the memory 55 or produces and stores new
data.
[0231] The signals from the sections 1, 2 and 3 include signals for
indicating a nozzle trouble and the remaining amount of ink in the
ink ejection section 1, the distance information (or
two-dimensional or three-dimensional shape data about the surface
of the object 7) from a reference position (e.g., the central
position of an end surface of the sensor) in the shape measuring
section 2 to a laser irradiation position on the surface of the
object 7 which is transmitted from the photoreceiver of the shape
measuring section 2, and position information from a position
sensor (not shown) for each direction in the scanning section
3.
[0232] FIG. 19 is a functional block diagram of the printing
apparatus 100B. The control section 5 executes the above-mentioned
corresponding programs in the CPU 53 to function as an operation
detail determining section 5A and a printing operation control
section 5B. The operation detail determining section 5A functions
to determine the details of operations of the ink ejection section
1 and the scanning section 3 in accordance with information about
the inclination of the surface of the object which is included in
the three-dimensional shape data obtained using the shape measuring
section 2. The printing operation control section SB functions to
control the operations of the ink ejection section 1 and the
scanning section 3 to perform the printing operation in accordance
with the details of operations determined by the operation detail
determining section 5A.
[0233] <External Input/Output Section>
[0234] The external input/output section 6 is provided inside the
printing apparatus body shown in FIG. 16 as a part thereof and/or
separately provided outside the printing apparatus body, and
functions as an interface to an operator of the printing apparatus.
More specifically, the external input/output section 6 comprises an
indicator (output portion) such as a monitor and a lamp, and an
input portion such as a keyboard, a teaching pendant and an
emergency stop button. The external input/output section 6 is used,
for example, to input printing start and stop signals, to indicate
information in the event of trouble, to operate an emergency stop
or the like in the event of trouble, and to rewrite the contents of
the memory 55. These signals are transmitted through internal buses
for interconnection between the external input/output section 6,
and the CPU 53, the memory 55 and the controllers 511, 521, 531, as
illustrated in FIG. 18.
[0235] <B2. Operation in Printing Apparatus>
[0236] The printing operation is performed by the above-mentioned
mechanisms. Specifically, the scanning section 3 causes the shape
measuring section 2 to scan the surface of the object 7, and the
shape measuring section 2 measures the shape of the surface of the
object 7. Based on the three-dimensional shape data obtained from
the result of the measurement in the shape measuring section 2, the
ink ejection section 1 ejects ink toward a print area of the object
7 during the scanning by the scanning section 3 through positions
spaced apart in the Z direction from ink striking positions
relative to the print area of the object 7. Thus, a desired image
is formed (or printed) on the surface of the object 7. These
sections 1, 2 and 3 are controlled by the above-mentioned control
section 5.
[0237] Operation in the printing apparatus 100B according to the
second preferred embodiment will be described with reference to the
flowchart of FIG. 20.
[0238] Upon initiating the operation in response to an operation
start instruction (Step S100), the printing apparatus 100B uses the
control section 5 to control the X-, Y-, Z- and R-direction
scanning sections 31, 32, 33 and 34 to return the scanning section
3 to its mechanical home position (Step S111). For example, the
topmost, leftmost and rearmost position to which the scanning
section 3 can move as viewed in FIG. 16 is defined as the home
position.
[0239] Next, the shape measuring section 2 is used to obtain the
three-dimensional shape data about the object 7. To this end, the
shape measuring section 2 in the print head section H scans the
surface of the object 7 through a predetermined distance (beyond a
printable range in the X direction) in a predetermined, positive or
negative, main scanning direction (e.g., from left (-X) to right
(+X) or in the +X direction as viewed in FIG. 16; assuming that the
main scanning direction is the X direction herein). The term "main
scanning direction" used herein means the direction in which the
print head section H moves continuously. While scanning in the
above-mentioned manner, the shape measuring section 2 measures a
distance (in the Z direction) from the shape measuring section 2 to
the laser irradiation position on the surface of the object 7 (Step
S112).
[0240] The operation of measuring the distance in the Z direction
at spots of measurement (the laser exposed positions) may be
performed either at predetermined time intervals or so as to
provide approximately equal spacings of measurement on the surface
of the object 7. Further, this operation may be performed at
irregular intervals. The two-dimensional position coordinates (X,
Y) of each spot of measurement are determined based on a position
detection result from an X-direction position detector (linear
encoder) 311 (FIG. 16) in the X-direction scanning section 31 and a
position detection result from a Y-direction position detector
(linear encoder) 321 (FIG. 16) in the Y-direction scanning section
32. Therefore, the printing apparatus 100B can establish
correspondence between the measurement value of the distance (in
the Z direction) from the shape measuring section 2 to the laser
irradiation position on the surface of the object 7 and the
two-dimensional position coordinates (X, Y) of the corresponding
spot of measurement, independently of the types of intervals of
measurement. This achieves the measurement of the shape of the
surface of the object 7 to provide the three-dimensional shape data
about the object 7.
[0241] If a distance measurement range in the Z direction is
sufficiently large, the shape measuring section 2 may scan at a
constant elevation. If the distance measurement range in the Z
direction is small, the shape measuring section 2 may scan while
being controlled in the Z direction so that the distance from the
surface of the object 7 does not exceed the distance measurement
range, based on the detected distance value. In this case, both a
detected current position value from a Z-direction position
detector (not shown) contained in the Z-direction scanning section
33 and the detected distance value are used to obtain the position
information about the surface of the object 7.
[0242] After the distance measurement for one line, a judgement is
made as to whether or not all of the distance measurements within
the target range of distance measurement (not less than the
allowable size of the object in the X and Y directions) is
completed (Step S113). If all of the distance measurements are
completed, the flow proceeds to Step S121. If all of the distance
measurements are not completed, the flow returns to Step S112 again
to perform the distance measurement for the next line.
[0243] For the distance measurement for the next line, the shape
measuring section 2 is moved to a distance measurement start
position for the next line, that is, a position shifted a
predetermined distance in the +Y direction (toward the viewer of
the figure) or a positive sub-scanning direction (orthogonal to the
main scanning direction) but not shifted in the main scanning
direction (X direction) from the distance measurement start
position for the current line (Step S114). Then, scanning in the
main scanning direction is started again. Repeating such an
operation provides the distance measurements within a predetermined
range of distance measurement. The detected values obtained by
these distance measurements and other data are stored in the memory
55.
[0244] After all of the distance measurements within the target
range of shape measurement are completed, the resultant data are
processed to produce the three-dimensional shape data about the
object 7 in a predetermined format (Step S121).
[0245] Next, print image data is obtained (Step S122). The print
image data is obtained by inputting through the external
input/output section 6 (such as a scanner). Alternatively, an
operator may selectively determine the print image data among a
plurality of data previously stored in the memory 55 or obtain the
single stored data without freedom of choice.
[0246] Then, matching is performed between the three-dimensional
shape data obtained by the measurement and the image data (print
image data) to be printed on the surface of the object. In other
words, the print image data is located and affixed to the
three-dimensional shape data about the surface of the object 7
(Step S123). This produces data affixed to the object. This process
may be performed by an operator manually inputting the data while
viewing an output portion (such as monitor) of the external
input/output section 6 or performed automatically in accordance
with a predetermined setting. The data affixed to the object is
produced based on the three-dimensional shape data obtained by
measurement and the image data to be printed on the surface of the
object. This enhances the precision of the produced data about
positions to achieve a high-quality printing process.
[0247] Thereafter, scanning control data and ink ejection control
data are produced (Step S124). More specifically, a scanning path
is determined, and data for scanning control about the positions,
velocities and accelerations of the X-, Y-, Z- and R-direction
scanning sections 31, 32, 33 and 34 for each unit of time is
produced. Also produced is data about the timing of ejection of the
ink from the ink ejection nozzles in corresponding relation to the
scanning control. The operation detail determining section 5A
produces these data (or determines the details of the
operation).
[0248] The object 7 described herein is of a pyramidal
configuration, as shown in FIG. 16. FIG. 21 is a top plan view of
the object 7 as viewed from the -Z direction. FIG. 22 is a side
view of the object 7 as viewed from the -Y direction. The closed
circles of FIGS. 21 and 22 indicate the ink striking positions in
exaggeration, with some of the actual ink striking positions
omitted, and the arrows of FIGS. 21 and 22 indicate the paths of
the nozzles when ejecting the ink toward the ink striking
positions.
[0249] When the spacing between the ink striking positions on a
face A1 of FIG. 21 in the main scanning direction (X direction) and
in the sub-scanning direction (Y direction) is assumed to be 1, the
ink is ejected onto faces A2 and A4 at a spacing of 1 in the main
scanning direction and at a spacing of cos .theta. in the
sub-scanning direction and to strike faces A3 and A5 at a spacing
of cos .theta. in the main scanning direction and at a spacing of 1
in the sub-scanning direction, where .theta. is an angle formed
between a vector normal to each inclined part of the object 7 and
the Z axis. Thus, ejection of the ink onto all of the faces so as
to always provide the same resolution as viewed in the direction
normal to the faces reduces difference in print quality depending
on the direction.
[0250] More specifically, the ink ejection operations in the main
scanning direction and in the sub-scanning direction may be
performed in a manner described with reference to FIGS. 3, 5 and
6.
[0251] First, the ink ejection operation (or the ejection pattern
control) in the sub-scanning direction (Y direction) is achieved in
a manner described with reference to FIG. 3. It should be noted
that the ejection head 50 shown in FIG. 3 corresponds to the print
head H of the second preferred embodiment. The stepwise travel
distance of the ink ejection section 1 relative to the object 7 in
the sub-scanning direction is determined in accordance with
information about the inclination of the surface of the object 7.
Therefore, consideration of information about the position in which
the object 7 is actually disposed achieves the printing operation
which ensures the uniform dot distribution more precisely.
[0252] The ejection pattern control in the main scanning direction
X is achieved in a manner described with reference to FIGS. 5 and
6. More specifically, adoptable methods of ejection pattern control
in the main scanning direction X includes: a method of changing the
travel velocity (main scanning velocity) V.sub..theta. of the print
head in accordance with the inclination angle .theta. so as to
satisfy V.sub..theta.=V.times.cos .theta. while fixing the ink
ejection frequency at the constant value f, as shown in FIG. 5; and
a method of changing the time intervals of ink ejection (i.e. the
driving frequency of the ejection nozzles) in accordance with the
inclination while fixing the main scanning velocity of the print
head H at the fixed value V, as shown in FIG. 6. These methods can
provide the dot-to-dot spacing which equals the constant value d on
the inclined surface independently of the inclination angle
.theta., to achieve the uniform dot distribution.
[0253] The high-quality printing operations (FIGS. 3, 5 and 6)
which provide a constant resolution on the inclined surface are
described hereinabove. Another operation for high-quality printing
will be described below.
[0254] First, the operation of controlling the ink ejection head
section 11 also in the Z direction at the time of printing will be
described. This operation is to prevent the deviation of the ink
striking positions and a problem known as satellite which result
from the structure of the ink ejection nozzles and the like in the
case of an increased distance (e.g. in the Z direction) between the
ink ejection nozzles and the ink striking positions. Such problems
are solved by controlling the scanning in the vertical direction (Z
direction) so that the ink ejection nozzles are always within a
predetermined distance from the ink striking positions. To this
end, the scanning control data for the X-, Y-, Z- and R-direction
scanning sections 31, 32, 33 and 34 may be produced so that the ink
ejection head section 11 moves within planes perpendicular to the
normal vectors to the respective faces of the object 7, or within
planes parallel to the respective faces of the object 7.
[0255] Another solution to the above-mentioned problems is to
select some ejection nozzles for use in printing among all of the
ejection nozzles of the ink ejection head section 11 of a
multi-nozzle arrangement, based on the distance between the
ejection nozzles and the object during the printing operation, to
perform the printing operation using the selected ejection nozzles.
This suppresses an error of the dot striking positions on the
object 7 within tolerance to prevent the deterioration in quality
of the printed image on the object 7.
[0256] This operation will now be described in detail with
reference to FIGS. 23A, 23B, 23C and 23D (in the sub-scanning
direction) and FIGS. 24A, 24B, 24C and 24D (in the main scanning
direction).
[0257] The ejection control in the sub-scanning direction Y is
described in detail hereinafter.
[0258] FIGS. 23A, 23B, 23C and 23D show the ejection control in the
sub-scanning direction Y. The paths of ink ejection from enabled
(or available) ejection nozzles (i.e. ejection nozzles allowed to
eject ink) are shown by the solid lines in FIGS. 23A, 23B, 23C and
23D, and the paths of ink ejection from disabled (or unavailable)
ejection nozzles (i.e. ejection nozzles inhibited from ejecting
ink) are shown by the broken lines.
[0259] In the process of moving the print head section H in the
sub-scanning direction Y, a minimum clearance (gap) between the
print head section H and the object 7 is maintained at a
predetermined value r.sub.0 to avoid the interference between the
print head section H and the object 7. The minimum clearance is a
minimum spacing between a part of the print head section H which is
opposed to the object 7 and a surface part of the object 7. To
maintain the minimum clearance at the predetermined value r.sub.0,
the Z-direction scanning section 33 is driven in accordance with
the scanning position of the print head section H to adjust the
vertical position of the print head section H in the Z
direction.
[0260] FIG. 23A shows printing on a horizontal part of the object
7. A distance h between each ejection nozzle and the object 7 is
determined, with the minimum clearance between the print head
section H and the object 7 maintained at the predetermined value
r.sub.0. As a result, all of the ejection nozzles satisfy the
relationship: h.ltoreq.h.sub.0 where h.sub.0 is an allowable
distance. Therefore, all of the ejection nozzles eject ink to
achieve efficient printing in the case of FIG. 23A.
[0261] FIG. 23B shows printing on a steeply inclined surface of the
object 7. The distance h between each ejection nozzle and the
object 7 is determined, with the minimum clearance between the
print head section H and the object 7 maintained at the
predetermined value r.sub.0. As a result, ejection nozzles for
ejection toward an upper part of the inclined surface satisfy
h<h.sub.0, whereas ejection nozzles for ejection toward a lower
part of the inclined surface satisfy h>h.sub.0. Therefore, the
ejection nozzles for ejection toward the lower part of the inclined
surface are disabled, and only the ejection nozzles for ejection
toward the upper part of the inclined surface are used for
printing.
[0262] FIG. 23C shows printing on the top of the object 7. The
distance h between each ejection nozzle and the object 7 is
determined, with the minimum clearance between the print head
section H and the object 7 maintained at the predetermined value
r.sub.0. As a result, ejection nozzles for ejection toward about
the top satisfy h<h.sub.0, whereas some of the ejection nozzles
for ejection toward the steeply inclined surface satisfy
h>h.sub.0. Therefore, these ejection nozzles which satisfy
h>h.sub.0 are disabled, and only the ejection nozzles for
ejection toward about the top are used for printing.
[0263] FIG. 23D shows printing on a gently inclined surface of the
object 7. The distance h between each ejection nozzle and the
object 7 is determined, with the minimum clearance between the
print head section H and the object 7 maintained at the
predetermined value r.sub.0. As a result, ejection nozzles for
ejection toward an upper part of the inclined surface satisfy
h.ltoreq.h.sub.0, whereas ejection nozzles for ejection toward a
lower part of the inclined surface satisfy h>h.sub.0. Therefore,
the ejection nozzles for ejection toward the lower part of the
inclined surface are disabled, and only the ejection nozzles for
ejection toward the upper part of the inclined surface are used for
printing. A smaller number of ejection nozzles are disabled in
printing on the gently inclined surface than in printing on the
steeply inclined surface. This provides efficient printing.
[0264] Thus, while moving the print head section H in the
sub-scanning direction Y, the printing apparatus 100B determines
the distance h in accordance with the position of the ejection
nozzles during the printing, and selects only the ejection nozzles
having the distance h falling within the range specified by the
allowable distance h.sub.0 to use the selected ejection nozzles for
printing. This allows the ink to strike the object 7 within the
tolerance of the target position, or suppresses the deterioration
of quality of the printed image. The selection of the ejection
nozzles is made using the information about the inclination of the
surface of the object which is included in the three-dimensional
shape data.
[0265] Next, the ejection control in the main scanning direction X
is described in detail hereinafter.
[0266] FIGS. 24A, 24B, 24C and 24D show the ejection control in the
main scanning direction X. The paths of ink ejection from enabled
ejection nozzles (i.e. ejection nozzles allowed to eject ink) are
shown by the solid lines in FIGS. 24A, 24B, 24C and 24D, and the
paths of ink ejection from disabled ejection nozzles (i.e. ejection
nozzles inhibited from ejecting ink) are shown by the broken
lines.
[0267] In the process of moving the print head section H in the
main scanning direction X, the minimum clearance between the print
head section H and the object 7 is maintained at the predetermined
value r.sub.0 to avoid the interference between the print head
section H and the object 7. In this case, the Z-direction scanning
section 33 is driven, as required, to adjust the vertical position
of the print head section H in the Z direction.
[0268] FIG. 24A shows printing on a horizontal part of the object
7. The distance h between each ejection nozzle and the object 7 is
determined, with the minimum clearance between the print head
section H and the object 7 maintained at the predetermined value
r.sub.0. As a result, all of the ejection nozzles satisfy the
relationship: h.ltoreq.h.sub.0. Therefore, all of the ejection
nozzles eject ink to achieve efficient printing in the case of FIG.
24A.
[0269] FIG. 24B shows printing on a gently inclined surface of the
object 7. The distance h between each ejection nozzle and the
object 7 is determined, with the minimum clearance between the
print head section H and the object 7 maintained at the
predetermined value r.sub.0. As a result, all of the ejection
nozzles satisfy h.ltoreq.h.sub.0. Therefore, all of the ejection
nozzles eject ink to achieve efficient printing in the case of FIG.
24B.
[0270] FIG. 24C shows printing on the top of the object 7. The
distance h between each ejection nozzle and the object 7 is
determined, with the minimum clearance between the print head
section H and the object 7 maintained at the predetermined value
r.sub.0. As a result, all of the ejection nozzles satisfy
h.ltoreq.h.sub.0. Therefore, all of the ejection nozzles eject ink
to achieve efficient printing in the case of FIG. 24C.
[0271] FIG. 24D shows printing on a steeply inclined surface of the
object 7. The distance h between each ejection nozzle and the
object 7 is determined, with the minimum clearance between the
print head section H and the object 7 maintained at the
predetermined value r.sub.0. As a result, ejection nozzles for
ejection toward an upper part of the inclined surface satisfy
h.ltoreq.h.sub.0, whereas ejection nozzles for ejection toward a
lower part of the inclined surface satisfy h>h.sub.0. Therefore,
the ejection nozzles for ejection toward the lower part of the
inclined surface are disabled, and only the ejection nozzles for
ejection toward the upper part of the inclined surface are used for
printing.
[0272] Thus, the printing apparatus 100B can select some ejection
nozzles for use in printing among all of the ejection nozzles of
the ink ejection head section 11 of a multi-nozzle arrangement,
based on the distance between each ejection nozzle and the object
during the printing operation, to perform the printing operation
using the selected ejection nozzles. The selection of the ejection
nozzles is made using the information about the inclination of the
surface of the object which is included in the three-dimensional
shape data.
[0273] As described hereinabove, when the object has a
three-dimensional shape, it is preferable, as in the present
invention, to previously make the distance measurements not only in
the main scanning direction but also in the sub-scanning direction
to obtain the three-dimensional position information, and
thereafter to segment the surface of the object into regions so
that the faces of the respective regions have the same (or
substantially the same) vector normal thereto (or has substantially
the same inclination) to plan the scanning control procedure and
the ink ejection procedure for each of the regions (having
substantially the same inclination).
[0274] In the example shown in FIG. 21 or 22, the CPU 53 produces
the control data based on the data stored in the memory 55 so that
printing (the ink ejection operation and the scanning operation)
starts from the home position P1 and is sequentially performed on
the faces A1, A2, A3, A4 and A5 of five segmented regions. The data
about the scanning velocity, the ink ejection timing and the travel
distance in the sub-scanning direction is set for each segmented
region. Such a setting operation is performed by the operation
detail determining section 5A.
[0275] In consideration for the continuity of the regions to be
printed, the printing apparatus 100B shall perform each of the ink
ejection operation on the faces A2 and A4 and the ink ejection
operation on the faces A3 and A5 during a continuous series of
scanning operations considered collectively as a unit. In other
words, the sequence of the ink ejection operation on the faces is:
(1) the face A1, (2) the faces A2 and A4, and (3) the faces A3 and
A5.
[0276] Referring again to the flowchart of FIG. 20, in Step S131,
printing starts based on the data produced in Step S124. To this
end, the ink ejection head section 11 is moved to the position of
the point P1 of FIG. 21 (Step S131). Next, the X-direction scanning
section 31 is controlled, and the Z-direction scanning section 33
is controlled to maintain the vertical clearance at a predetermined
distance. Then, scanning for one line is performed in the main
scanning direction. In synchronism with the scanning, the ink
ejection nozzles 111N, 112N, 113N and 114N eject ink toward a first
region to be printed, based on the above-mentioned data (Step
S132). If it is not judged that all of the printing is completed in
Step S133, the ink ejection head section 11 moves to the next
printing start position (Step S134) to start printing in the next
main scanning line.
[0277] In accordance with the ink ejection operation and the
scanning operation which are determined for each of the segmented
regions A1 to A5, such a printing operation is performed in the
above-mentioned sequence of the segmented regions: (1) A1, (2) A2
and A4, and (3) A3 and A5.
[0278] If it is judged that all of the printing is completed in
Step S133, the printing operation is terminated (Step S199).
[0279] As described hereinabove, the printing apparatus 100B
according to this preferred embodiment measures the shape of the
surface of the object 7, obtains the three-dimensional shape data
about the object 7 based on the result of measurement, determines
the details of the operations of the ink ejection section 1 and the
scanning section 3 in accordance with the information about the
inclination of the surface of the object 7 which is included in the
obtained three-dimensional shape data, and controls the operations
of the scanning section 3 and the ink ejection section 1 in
accordance with the details of the operations thereof to perform
the printing operation. Printing in accordance with the information
obtained by measurement on the inclination of the surface of the
object 7 achieves a high-quality printing process.
[0280] Although the print area of the object 7 having a simple
pyramidal shape is segmented into the plurality of regions A1 to A5
in the above description, the surface of the object 7, if having a
complicated shape, may be segmented into a plurality of regions
which two-dimensionally approximate the surface shape of the object
7. In other words, the printing target surface of the object 7 may
be approximated by n faces (polygonal faces) (where n is an
integer) based on the three-dimensional shape data. If the surface
of the object 7 has a smoothly rugged shape, the surface shape may
be represented as a set of polygonal faces by processing the data
about the surface. These polygonal faces are formed by segmentation
such that a region in which a normal vector to the surface of the
object 7 at each position lies within a predetermined allowable
range (or a region having substantially the same inclination) is
defined as the same segmented region (polygonal face) and a region
in which the normal vector at each position exceeds the
predetermined allowable range (or a region having a different
inclination) is defined as a different region (polygonal face).
[0281] <C. Third Preferred Embodiment>
[0282] Although it is assumed that the three-dimensional shape data
about the three-dimensional object is completely unknown in the
second preferred embodiment, a third preferred embodiment of the
present invention will now be described assuming that
three-dimensional shape model data representing the
three-dimensional shape of the object is previously known and
obvious. The three-dimensional shape model data to be prepared need
not be so detailed but may be expressed to the extent that the
overview of the object is appreciable.
[0283] For printing on the three-dimensional object according to
the third preferred embodiment, the print area of the object 7 is
segmented into a plurality of regions A1 to A5 which
two-dimensionally approximate the surface shape of the object 7
based on the previously given three-dimensional shape model data.
Then, the shape measuring section 2 measures the three-dimensional
shape of each segmented region in detail, and the control section 5
determines the details of the ink ejection operation and the
details of the scanning operation to perform the printing
operation. The operations (of measurement, determination and
printing) are performed for each of the segmented regions to reduce
the amount of data to be handled collectively. This is particularly
useful when the capacity of the memory 55 is not large enough to
handle the data about the entire print area at a time as in the
second preferred embodiment.
[0284] The printing apparatus according to the third preferred
embodiment is different in operation from but similar in physical
construction to the printing apparatus of the second preferred
embodiment. The operation of the printing apparatus of the third
preferred embodiment will now be principally described.
[0285] FIG. 25 is a flowchart showing the operation according to
the third preferred embodiment.
[0286] Initially, in Step S200 of FIG. 25, the object 7 is fixed in
predetermined position and direction on the turntable 341, and the
printing operation is initiated.
[0287] Next, a corresponding file (including a description of the
three-dimensional shape data about the object) stored in the memory
55 or the auxiliary storage 56 is opened to obtain the
three-dimensional shape model data about the object (Step S211).
Then, the print image data is obtained (Step S212). This step of
obtaining the print image data is similar in operation to Step S122
(FIG. 20).
[0288] Based on the three-dimensional shape model data, the surface
shape of the object 7 in the print area is approximated by n
segmented regions (polygonal faces) (where n is an integer). Then,
the sequence of distance measurement of the segmented regions (and
the sequence of printing on the segmented regions) is established
(Step S213). It is assumed that the faces A1, A2, A3, A4 and A5
shown in FIG. 21 are to be subjected to the distance measurement
and printing in the sequence named.
[0289] When the segmented region having the face A1 is selected
first as a target segmented region, the steps to be described below
are performed on the segmented region having the face A1, as shown
in FIG. 26.
[0290] In Step S221, the X-, Y-, Z- and R-direction scanning
sections 31, 32, 33 and 34 are driven to move the shape measuring
section 2 to the distance measurement start position (the point P1
for the face A1). The distance measurement of the target segmented
region starts from the position P1, and the distance measurement is
made on the face A1 (Steps S222 to S224). This operation of
measurement is similar to that of the second preferred
embodiment.
[0291] Next, the data obtained by the measurement is processed to
produce the three-dimensional shape data about the measured region
of the object 7 in a predetermined format (Step S231).
[0292] In Step S232, matching is performed between the actual
three-dimensional shape data obtained in Steps S221 to S224 and
Step S231 and the three-dimensional shape model data obtained in
Step S211.
[0293] More specifically, the details of the matching operation are
selectable depending on the level of reliability of the
three-dimensional shape model data.
[0294] For example, when the three-dimensional shape model data has
a low level of reliability (including the case where the
three-dimensional shape model data is data about the overview of
the object 7), the three-dimensional shape data produced based on
the result of measurement may be used in place of the
three-dimensional shape model data as reference data for printing
operation for the segmented region of interest.
[0295] On the other hand, when the three-dimensional shape model
data has a high level of reliability, the matching of data about
the position and posture of the object 7 is performed by
calculating the amount of deviation of the three-dimensional shape
data (measured value) resulting from the result of measurement from
the three-dimensional shape model data (theoretical value). The
amount of deviation may be calculated by establishing
correspondence between the coordinates of the three-dimensional
shape model and the actual position obtained from the
three-dimensional shape data, and thereafter the three-dimensional
shape data may be rewritten in consideration for the amount of
deviation from the three-dimensional shape model data (theoretical
value). If the object 7 placed on the turntable 341 is deviated at
a predetermined angle from a desired position, this process can
correct the deviation to provide correct three-dimensional shape
data. Such an adjustment provides higher-precision printing.
Alternatively, the scanning section 3 (particularly the turntable
341 of the R-direction scanning section 34) may be driven to
correct the angle of deviation of the three-dimensional shape data
(measured value) from the three-dimensional shape model data
(theoretical value) to make a fine adjustment so that the actual
position of the object 7 conforms to the three-dimensional shape
model data. Thereafter, the matching is performed between the
three-dimensional shape data and the print image data, as in Step
S123.
[0296] After the matching operation (Step S232), the scanning
control data and the ink ejection control data are produced (Step
S233), as in the second preferred embodiment. Produced in this step
is the data about only the segmented region having been subjected
to the distance measurement (the face A1 in this case) in the
entire print area. Based on the produced data, the ink ejection
head section 11 is moved to the printing start position (Step
S241). The X-direction scanning section 31 is controlled, whereas
the Z-direction scanning section 33 is also controlled to maintain
the vertical clearance at the predetermined distance. Then,
scanning for one line is performed in the main scanning direction.
In synchronism with the scanning, the ink ejection nozzles 111N,
112N, 113N and 114N eject ink toward the region to be printed
first, based on the above-mentioned data (Step S242). A judgement
is made as to whether or not all of the printing on the
predetermined region is completed (Step S243). If it is not judged
that all of the printing is completed, the ink ejection head
section 11 is moved to the printing start position of the next line
(Step S244) to start printing in the next main scanning line. This
printing operation is repeated until it is judged that all of the
printing on the predetermined region is completed in Step S243.
This completes the printing operation on the face A1 of the first
target segmented region.
[0297] In step S251 (FIG. 25), a judgement is made as to whether or
not printing on the entire print area is completed. In this case,
since other segmented regions are left unprinted, the next
segmented region A2 determined in Step S213 is selected as the
target segmented region (Step S252). The flow returns to Step S221
to start the control.
[0298] The above described steps are repeated to perform similar
operations of measurement and printing on the remaining segmented
regions A3 to A5. A region containing no print data (or a region
not to be printed) may be skipped.
[0299] If it is judged that printing is completed on all of the
segmented regions in Step S299, the operation is terminated.
[0300] <D. Fourth Preferred Embodiment>
[0301] A fourth preferred embodiment according to the present
invention will be described. The fourth preferred embodiment is
useful when the surface of the object 7 is less rugged in the
sub-scanning direction to allow successive printing on a plurality
of adjacent segmented regions arranged in the sub-scanning
direction (or when the sequence of printing on the surfaces to be
printed is not discrete but successive in one direction). For
example, it is useful for printing on an object 7c having a
triangular cross-sectional configuration, as illustrated in FIG.
29. The object 7a has two inclined surfaces F1 and F2 whose
inclination does not change in the sub-scanning direction (Y
direction). For purposes of simplification, the inclined surface F1
is selected as the print area among the two inclined surfaces F1
and F2, and is segmented into a plurality of rectangular regions
(R1, R2, R3, . . . ) having a predetermined width in the
sub-scanning direction. The operation will be described with
reference to the flowcharts of FIGS. 27 and 28.
[0302] The step of starting the printing operation (Step S300) to
the step of segmentation into the regions using the
three-dimensional shape model data (Step S313) are similar to Steps
S200 to S213 of the third preferred embodiment. In Step S313, the
sequence of distance measurement of the segmented regions is
established so as to be successive in the sub-scanning direction (Y
direction). The sequence of distance measurement of the segmented
regions is established as R1, R2, R3, . . . in this preferred
embodiment. The sequence of printing on the segmented regions is
identical with the sequence of distance measurement.
[0303] Then, as in the third preferred embodiment, the X-, Y-, Z-
and R-direction scanning sections 31, 32, 33 and 34 are moved to
the distance measurement start position (Step S321), and the
distance information is obtained (Steps S322 to S324). The
operation of distance measurement is performed on the first
measurement target region R1. Based on the result of measurement,
the three-dimensional shape data is produced (Step S331). FIG. 30A
shows the operation of performing main scanning in the main
scanning direction to make the distance measurement on the
segmented region R1 by the shape measuring section 2. The matching
is performed between the three-dimensional shape data and the
three-dimensional shape model data to reflect the actual shape in
the model, and the matching is performed between the
three-dimensional shape data and the print image data (Step S332).
In this step, a fine adjustment is made, as required, so that the
actual orientation of the object 7 conforms to the
three-dimensional position coordinates of the thee-dimensional
shape model. Then, the scanning control data and the ink ejection
control data are produced (Step S333). Produced in this step is the
data about only the segmented region R1 having been subjected to
the distance measurement and to be printed currently. Based on the
produced data, the ink ejection head section 11 is moved to the
printing start position of the segmented region R1 in Step S341.
The steps described hereinabove are similar to those of the third
preferred embodiment.
[0304] At this point, as illustrated also in FIG. 16, the distance
measurement position of the shape measuring section 2 is spaced a
predetermined distance from the ink striking position forwardly in
the sub-scanning direction (Y direction). FIG. 31 conceptually
illustrates such a positional relationship between the distance
measurement position and the ink striking position. With reference
to FIG. 31, a distance D between the ink striking position Q1 of
the ink ejected from the ink ejection head section 11 and the
distance measurement position Q2 of the shape measuring section 2
is determined by the positional relationship between the ink
ejection section 1 and the shape measuring section 2 (displacement
sensor) in the print head section H. Such a positional relationship
may be utilized to simultaneously perform the printing and the
distance measurement during the same scanning in the subsequent
step (Step S342), thereby achieving efficient distance measurements
in unprinted regions (segmented regions R2, R3, . . . ) forward of
the printing target region. For purposes of simplification, the ink
ejection head section 11 is shown in FIG. 31 as having a
single-nozzle arrangement, with the width W of the segmented region
R1 in the sub-scanning direction equaling the distance D in the
sub-scanning direction between the distance measurement position
and the ink striking position. In this case, at the time when the
shape measuring section 2 moves to the measurement start position
of the next segmented region R2 after the completion of the
distance measurement of the segmented region R1, the ink ejection
section 1 reaches the printing start position of the segmented
region R1 having been measured (See FIG. 31).
[0305] Next, printing is performed on the segmented region R1.
While the Z-direction scanning section 33 is controlled to maintain
the distance in the Z direction between the print head section H
and the object 7 at a predetermined distance (e.g. maintain the
above-mentioned minimum clearance at r.sub.0), the X-direction
scanning section 31 is controlled to scan one line in the main
scanning direction (X direction). In synchronism with this
operation, the C, M, Y and K ink ejection nozzles 111N, 112N, 113N
and 114N eject ink toward the segmented region R1 serving as the
first printing target region, based on the above-mentioned data.
Additionally, in synchronism with this scanning operation, the ink
ejection operation is performed, and the shape measuring section 2
make the distance measurement on the next segmented region R2 (Step
S342). This measurement is made at a position which is spaced the
predetermined distance D apart in the sub-scanning direction from
the ink striking position used in printing on the segmented region
R1. The distance D is determined by the arrangement in the print
head section H as above described. The resultant measured distance
data are sequentially stored in the memory 55 of the control
section 5. FIG. 30B schematically shows such an operation in which
while printing is performed on the segmented region R1, the
measurement is made on the next segmented region R2.
[0306] Then, a judgement is made as to whether or not printing on
the predetermined region (the segmented region R1 in this case) is
completed (Step S343). If the printing is not completed, the
above-mentioned scanning operation in the main scanning direction
is repeated. In this case, the ink ejection head section 11 moves
to the next printing start position (Step S344), and the printing
of the next main scanning line and the measurement are
initiated.
[0307] If it is judged in Step S343 that the printing on the region
R1 is completed, a judgement is made as to whether or not printing
on all of the segmented regions included in the entire print area
is completed (Step S351). Since segmented regions to be printed
remain unprinted in this case, the flow proceeds to Step S352 in
which the next segmented region R2 is selected as a segmented
region to be printed in accordance with the sequence determined in
Step S313. At the same time, the next segmented region R3 is
selected as a segmented region to be measured.
[0308] Next, the flow returns again to Step S331 in which the
three-dimensional shape data about the segmented region R2 to be
printed next which is selected in Step S352 is produced, and
printing is performed on the segmented region R2 in the
above-mentioned manner. FIG. 30C schematically shows such an
operation in which while printing is performed on the segmented
region R2, the measurement is made on the next segmented region
R3.
[0309] Subsequently, similar operations are repeated in succession
to sequentially measure and print on the segmented regions. If it
is judged that all of the printing is completed in Step S351 during
the repetition process, the control and operation are terminated
(Step S399).
[0310] As described hereinabove, for printing on the
three-dimensional object, the printing apparatus of this preferred
embodiment simultaneously performs the operation of printing on a
predetermined segmented region selected among the plurality of
segmented regions and the operation of distance measurement of the
segmented region adjacent to the predetermined segmented region, to
enhance the efficiency of the operations of printing and
measuring.
[0311] In the segmentation of the print area into the regions using
the three-dimensional shape model data (or the establishment of the
segmented regions) in Step S313, it is preferable that the width W
of each segmented region in the sub-scanning direction is equal to
or less than the distance D (See FIG. 31) in the sub-scanning
direction between the distance measurement position of the shape
measuring section 2 and the ink striking position of the ink
ejection section 1. In the above-mentioned case, the surface F1 to
be printed which has the same inclination in the Y direction is
segmented into the plurality of regions R1, R2, R3, . . . each
having the width W in the sub-scanning direction which satisfies
the above condition, i.e., which is equals to the distance D in the
sub-scanning direction between the distance measurement position of
the shape measuring section 2 and the ink striking position of the
ink ejection section 1 (W=D). In the case where W<D, the
printing apparatus may be operated so that, at the time of
completion of printing on the predetermined segmented region (e.g.,
the segmented region R1), the distance measurement position of the
shape measuring section 2 reaches a position forward of the next
region to be printed (e.g., the segmented region R2), and the
distance measurement of at least one forward segmented region
(e.g., the segmented region R2) is completed. Thus, the printing
path is preferably planned also in Step S313 so that the distance
measurement of at least one unprinted region is completed whenever
it is judged in Step S343 that printing on the current printing
target segmented region is completed. In this case, at the end of
printing on the predetermined segmented region, the distance
measurement of the next printing target segmented region is
completed. This allows the flow to proceed without a break to Step
S331 in which the three-dimensional shape data about the next
printing target segmented region is produced based on the result of
measurement.
[0312] For the multi-nozzle arrangement as illustrated in FIG. 32,
a relationship to be described below should be considered regarding
the distance D between the striking position Q1 of ink ejected from
a nozzle N2 and the distance measurement position Q2 of the shape
measuring section 2, the nozzle N2 being the nearest active nozzle
to the shape measuring section 2 of all nozzles N1 to N4 in a
nozzle array of the ink ejection head section 11. (The term "active
nozzle" used herein means that the nozzle ejects ink.) In the
illustration shown in FIG. 32, it is assumed that the nozzle Ni
which is the nearest to the shape measuring section 2 of all of the
nozzles in the nozzle array is disabled because of the
circumstances described with reference to FIGS. 23A to 23D or the
like.
[0313] With such a multi-nozzle arrangement, the printing operation
throughout the width (w1.times.m) of the segmented region R1 is
achieved by the scanning operation throughout the width w1 which
involves multi-step (or plural) movements in the sub-scanning
direction, where m is the number of active nozzles arranged in a
linear array in the sub-scanning direction, for example m=3 when
three nozzles N2, N3 and N4 eject ink. Thus, the start of the
printing operation on the object in the case of the multi-nozzle
arrangement may lag a distance (w1.times.(m-1)) in the sub-scanning
direction behind the start of the printing operation in the case of
the single-nozzle arrangement (in other words, the printing
operation in the case of the multi-nozzle arrangement may start
after the ink ejection head section 11 moves the distance
(w1.times.(m-1)) into the printing target segmented region).
Therefore, when m nozzles eject ink, the distance measurement
position Q2 of the shape measuring section 2 is required to be
present a distance (W-w1.times.(m-1)), rather than the distance W,
farther forward than the striking position Q1 of ink ejected from
the ink ejection head section 11 which is the nearest to the shape
measuring section 2. Preferably, the width W is set so that the
distance D is not less than the distance (W-w1.times.(m-1)). In
other words, the width W of each segmented region in the
sub-scanning direction is set at a value (D+w1.times.(m-1)) or
smaller. In general, W=w1.times.m, in which case
(W-w1.times.(m-1))=w1. In view of the case where all of the nozzles
are used, m is defined as the maximum number of nozzles.
[0314] The multi-nozzle arrangement requires not only the scanning
operation which involves the simultaneous operations of printing
and measurement but also the scanning operation to be performed
only for the operation of measurement. However, the operations of
measurement and printing are performed concurrently during the
scanning operation throughout the width w1 included in the entire
width (w1.times.m) in the sub-scanning direction. This is also
efficient in operation.
[0315] Although only the inclined surface F1 is selected as the
print area in the above description for purposes of simplification,
the other inclined surface F2 may be additionally selected as the
print area. In this case, the inclined surface F2 may be segmented
into a plurality of rectangular regions (R11, R12, R13, . . . )
having a predetermined width in the sub-scanning direction, and
similar processes may be performed.
[0316] <E. Modifications>
[0317] Although the preferred embodiments of the present invention
have been described hereinabove, the present invention is not
limited to the above description.
[0318] <E1. Fine Pitch p>
[0319] For example, the fine pitch p serving as the minimum unit of
distance the ejection head 50 is driven to move in the sub-scanning
direction Y is set at p=d/10 based on the spacing d between the
dots to be formed on the surface of the object 9 in the first
preferred embodiment and the like. However the fine pitch p is not
limited to this value.
[0320] Setting the fine pitch p at a smaller value, e.g., p=d/100
reduces the error of the spacing in the sub-scanning direction Y
between the dots printed on the inclined surface, thereby to allow
the spacing between the dots printed on the inclined surface to
more precisely approach the spacing d between the dots printed on
the horizontal surface. In other words, setting the fine pitch p at
a smaller value provides an accordingly higher level of uniformity
of the dots in the sub-scanning direction to achieve
higher-definition printing.
[0321] On the other hand, setting the fine pitch p at a smaller
value causes an accordingly smaller amount of stepwise movement of
the ejection head 50 in the sub-scanning direction Y, resulting in
the reduction in printing efficiency.
[0322] It is therefore preferable that a setting of the minimum
unit of distance the ejection head 50 is driven to move by the
sub-scanning direction driver 20 is freely changeable, and the
controller 43 determines the fine pitch p to be set for the
printing operation in accordance with a print quality and a
printing velocity which are desired by a user, to transmit the fine
pitch p to the sub-scanning direction driver 20. This provides a
user-intended balance between the print quality and the printing
velocity which are in trade-off relationship.
[0323] <E2. Re-measurement>
[0324] In the second preferred embodiment, one operation of
measurement is performed for each of the positions of the object 7
to produce the three-dimensional shape data. However, the present
invention is not limited to this. An additional measurement (a
total of at least two measurements) may be made on some regions to
measure the surface shape of the object 7, thereby obtaining the
three-dimensional shape data.
[0325] FIG. 33 is a flowchart showing such a modification of the
operation. Only the steps to which modification is made in the
flowchart of FIG. 20 are illustrated in FIG. 33. Steps S121, S122,
S123 and S124 of FIG. 33 are similar in operation to those of FIG.
20. The flowchart shown in FIG. 33 includes steps (Steps S401, S402
and S403) different in operation from the flowchart of FIG. 20
between Steps S121 and S122.
[0326] More specifically, after the three-dimensional shape data is
produced based on the result of the first measurement (Step S121),
an edge region is extracted based on the three-dimensional shape
data (Step S401). The second measurement is made on the extracted
edge region (Step S402). Thereafter, the three-dimensional shape
data is reproduced based on the second measurement (Step S403). The
subsequent steps may be performed based on the re-produced
three-dimensional shape data.
[0327] The second measurement (Step S402) can provide more detailed
data. The second measurement is preferably higher in precision than
the first measurement. Such a higher-precision measurement is
achieved by slower scanning in the main scanning direction and/or
by scanning in the sub-scanning direction using a smaller travel
distance.
[0328] This modification can provide more precise three-dimensional
shape data about the edge region to correctly assign the print
image data obtained in Step S122 to a desired position of the
object 7. Additionally, since the printing operation (Steps S131 to
S134) are performed based on the more precise three-dimensional
shape data, a desired image may be printed in a correct position on
the object 7.
[0329] In particular, if there are changes in pattern, texture and
color in the edge region of the printing image, a print deviation
in the edge region remarkably deteriorates the quality of the
printing process. In such a case, the above-mentioned
re-measurement is applied to suppress the print deviation in the
edge region to achieve a high-quality printing process.
[0330] Regions to be selected for the second measurement (or
regions requiring more detailed three-dimensional shape) include a
surface-to-surface junction such as the abovementioned edge, a
boundary line and an end point of the print area, and a region
including other characteristic points.
[0331] In the third and fourth preferred embodiments, the
three-dimensional shape data (three-dimensional shape model data)
is obtained before the start of the measurement. Thus, the printing
apparatus may extract the edge region based on the
three-dimensional shape data (three-dimensional shape model data),
and perform slower main scanning or sub-scanning using a smaller
travel distance in the edge region than in other regions during the
operation of distance measurement in Steps S221 to S224 (FIG. 26),
thereby to obtain more detailed shape data. In this case, the
measurement for obtaining higher precision (more detailed) data
requires longer time. However, the increase in length of time for
measurement may be minimized by restricting the region to be
measured for such more detailed data to a particular region such as
the edge region.
[0332] <E3. Shape Measuring Section 2>
[0333] Although the displacement sensor of the shape measuring
section 2 is mounted as part of the print head section H to the
output shaft 331 of the Z-direction scanning section 33 in the
above preferred embodiments, the present invention is not limited
to such an arrangement. For example, if the shape measuring section
2 has a sufficiently wide detectable distance range and includes a
displacement sensor of a long distance detection type, a
modification as illustrated in FIG. 34 may be used in which the
shape measuring section 2 includes a displacement sensor 2B mounted
on a side surface of the Z-direction scanning section 33 so as not
to move in the Z direction. The printing method of the present
invention is also implemented by such a modification.
[0334] In the above preferred embodiments, the displacement sensor
of the shape measuring section 2 is a sensor for detecting the
distance between the surface of the object at a position (point) to
which a spot light is projected and the sensor. However, the
present invention is not limited to this. A displacement sensor
capable of simultaneously obtaining distance information about a
plurality of positions may be employed.
[0335] For example, a two-dimensional scanning type optical sensor
(referred to hereinafter as a "first type two-dimensional
displacement sensor") containing a mechanism (e.g., a rotary
polygon mirror) for scanning in the X direction the spot light
directed from the phototransmitter 21 onto the object 7 may be used
as the shape measuring section 2. The first type two-dimensional
displacement sensor detects position information (X coordinate
values) about points of measurement irradiated with the spot light
and arranged in the scanning direction (X direction) and
information about the distances in the Z direction obtained by the
above-mentioned method in combination, thereby to provide
two-dimensional position information about an X-Z plane including
the line scanned by the spot light and extending in the X
direction.
[0336] Alternatively, a displacement sensor (referred to
hereinafter as a "second type two-dimensional displacement sensor")
may be used which comprises the phototransmitter 21 for emitting
slit laser light and the photoreceiver 22 including an area sensor
(CCD, PSD or the like) and which uses the light-section method to
obtain the two-dimensional position information about an X-Z plane
from the light diffuse-reflected from the surface of the object 7.
The second type two-dimensional displacement sensor obtains the
two-dimensional position information about the X-Z plane, based on
the triangulation technique.
[0337] The use of the first or second type two-dimensional
displacement sensor eliminates the need to cause the shape
measuring section 2 to scan in the X direction for the measurement
within its measurable range, to reduce the time required for
measurement. For measurement beyond the measurable range of the
displacement sensor in the X direction, the operation of moving the
displacement sensor to a predetermined measurement position may be
intermittently repeated several times, thereby providing the
two-dimensional position information about the X-Z plane.
Therefore, there is no need to cause the shape measuring section 2
to scan continuously in the X direction.
[0338] When the first or second type two-dimensional displacement
sensor having a long measurable distance range in the Z direction
is used as the displacement sensor of the shape measuring section
2, there is no need to cause the displacement sensor itself to scan
in the X direction. Additionally, the movement of the object 7 and
the print head section H relative to each other is accomplished by
driving the object 7 in the Y direction, as in the printing
apparatus 100B. In such a case, a displacement sensor 2C may be
mounted to an immovable component such as the cover CV, as
illustrated in FIG. 35, to achieve a similar operation of
measurement.
[0339] The shape measuring section 2 including the first or second
type two-dimensional displacement sensor may be provided in an
orientation rotated 90.degree. from the position shown in FIG. 16
or 34 about the Z axis, in which case two-dimensional position
information about a Y-Z plane is obtained without scanning in the Y
direction.
[0340] The second type two-dimensional displacement sensor may be
developed into a mechanism capable of scanning the slit light
emitted from the phototransmitter 21 in a direction (e.g., the Y
direction) perpendicular to a sectional plane (e.g., the X-Z
plane). This mechanism can determine the thee-dimensional shape of
the surface of the object 7 by the use of only the sensor itself,
based on the information (Y coordinate value) about the positions
arranged in the scanning direction and the detected two-dimensional
position information (about the X-Z plane) (an example of which is
a non-contacting three-dimensional shape input machine available as
VIVID700 and the like from MINOLTA CO., LTD.). In such a mechanism,
if the displacement sensor of the shape measuring section 2 has a
sufficiently wide detectable range in the Z direction and can
detect a distance from a sufficiently distant position, the
displacement sensor may be fixed in a position shown in FIG. 35 to
detect the three-dimensional shape of the surface of the object 7
without moving the scanning section 3. The three-dimensional shape
measuring sensor is not limited to those of the above-mentioned
types but may be of other types. For example, sensors for measuring
the three-dimensional shape of the object 7 by the techniques of
the stereo method, the moir method and interferometry may be
used.
[0341] In the above-mentioned preferred embodiments, the shape
measuring section 2 includes the displacement sensor which obtains
the distance information about each single point on the surface of
the object 7 and which is caused to scan for measurements. However,
the use of the above-mentioned two-dimensional displacement sensors
and three-dimensional shape measuring sensors changes the
flowcharts of FIGS. 20, 26 and 28 more or less.
[0342] For example, a two-dimensional displacement sensor for
measuring a distance in the X-Z plane, when used, does not need the
scanning operation in the main scanning direction in Steps S112,
S222 and S322 but can make the measurement on the X-Z plane while
standing still in a predetermined position. The same is true for
the measurement in Step S342.
[0343] The use of a two-dimensional displacement sensor for
measuring a distance in the Y-Z plane, which can obtain all of the
information about the Y direction during one operation of distance
measurement, eliminates the need to provide Steps S113 and S114 in
the second preferred embodiment (FIG. 20). Even if a plurality of
operations of distance measurement are required for the
displacement sensor to obtain all of the information about the Y
direction (e.g., when a short length is measured in the Y direction
or when interpolation is needed because of a wide pitch of
measurement), this two-dimensional displacement sensor can reduce
the number of times of movement in Steps S114, S224 and S324 of the
second, third and fourth preferred embodiments, as compared with
the sensor which measures a distance at one point during one
operation of distance measurement. The distance measurement in Step
S342 which are made at a plurality of positions during one
operation of main scanning may be performed when required between
Steps S342 and S344.
[0344] When the shape measuring section 2 includes a
three-dimensional measuring sensor capable of measuring the shape
of the entire area to be distance-measured during one operation of
measurement without the need to cause the sensor itself to scan,
the Steps S112, S113, S114 of the second preferred embodiment (FIG.
20) are replaced with one step of measuring the three-dimensional
shape. Even if a plurality of operations of distance measurement
are required to measure the shape of the entire region to be
distance-measured (e.g., when a distance measurable range is
small), this sensor can reduce the number of times of operations in
Steps S112, S114, Steps S222, S224 and Steps S322, S324 of the
second, third and fourth preferred embodiments, as compared with
the sensor which measures a distance at one point during one
operation of distance measurement. The same is true for the
distance measurement in Step S342.
[0345] In the third and fourth preferred embodiments, the object 7
is fixed in the predetermined position and orientation on the
turntable 341 before the printing is initiated. The third and
fourth preferred embodiments, however, are adaptable for the
printing with the object 7 mounted in a position (and/or
orientation) different from the intended position (and/or
orientation).
[0346] More specifically, starting from the mechanical home
position, the distance measurement is made on a region large enough
to obtain the characteristic of the object. Next, the
three-dimensional shape data about the region is produced, and
matching is performed between the produced three-dimensional shape
data and the prepared three-dimensional shape model data, whereby
the position and orientation of the object 7 are grasped. Based on
the result of detection of the position, the scanning section 3 is
controlled to change the orientation of the object 7 or to change
the distance measurement start position. Alternatively, the data
may be rewritten by bringing the coordinates of the
three-dimensional shape model into correspondence with the actual
position of the object 7. These steps may be additionally executed,
for example, after Step S211 in the third preferred embodiment or
after Step S311 in the fourth preferred embodiment.
[0347] In the above-mentioned preferred embodiments, the scanning
section 3 has three degrees of freedom of linear movement and one
degree of freedom of rotation. However, the printing apparatus
according to the present invention may be equipped with three or
more degrees of freedom of linear movement and three or more
degrees of freedom of rotation to serve as a general-purpose
printing apparatus. On the contrary, the number of degrees of
freedom may be reduced to limit the uses of the printing
apparatus.
[0348] While the invention has been described in detail, the
foregoing description is in all aspects illustrative and not
restrictive. It is understood that numerous other modifications and
variations can be devised without departing from the scope of the
invention.
* * * * *